Direct determination of the ionization energies of PtC, PtO, and PtO2 with VUV radiation

Photoionization efficiency curves were measured for gas-phase PtC, PtO, and PtO2 using tunable vacuum ultraviolet (VUV) radiation at the Advanced Light Source. The molecules were prepared by laser ablation of a platinum tube, followed by reaction with CH4 or N2O and supersonic expansion. These measurements provide the first directly measured ionization energy for PtC, IE(PtC) = 9.45 +/- 0.05 eV. The direct measurement also gives greatly improved ionization energies for the platinum oxides, IE(PtO) = 10.0 +/- 0.1 eV and IE(PtO2) = 11.35 +/- 0.05 eV. The ionization energy connects the dissociation energies of the neutral and cation, leading to greatly improved 0 K bond dissociation energies for the neutrals: D0(Pt-C) = 5.95 +/- 0.07 eV, D0(Pt-O) = 4.30 +/- 0.12 eV, and D0(OPt-O) = 4.41 +/- 0.13 eV, as well as enthalpies of formation for the gas-phase molecules DeltaH(0)(f,0)(PtC(g)) = 701 +/- 7 kJ/mol, DeltaH(0)(f,0)(PtO(g)) = 396 +/- 12 kJ/mol, and DeltaH(0)(f,0)(PtO2(g)) = 218 +/- 11 kJ/mol. Much of the error in previous Knudsen cell measurements of platinum oxide bond dissociation energies is due to the use of thermodynamic second law extrapolations. Third law values calculated using statistical mechanical thermodynamic functions are in much better agreement with values obtained from ionization energies and ion energetics. These experiments demonstrate that laser ablation production with direct VUV ionization measurements is a versatile tool to measure ionization energies and bond dissociation energies for catalytically interesting species such as metal oxides and carbides.     

Infrared spectrum of NH4+(H2O): evidence for mode specific fragmentation

The gas phase infrared spectrum (3250-3810 cm-1) of the singly hydrated ammonium ion, NH4+(H2O), has been recorded by action spectroscopy of mass selected and isolated ions. The four bands obtained are assigned to N-H stretching modes and to O-H stretching modes. The N-H stretching modes observed are blueshifted with respect to the corresponding modes of the free NH4+ ion, whereas a redshift is observed with respect to the modes of the free NH3 molecule. The O-H stretching modes observed are redshifted when compared to the free H2O molecule. The asymmetric stretching modes give rise to rotationally resolved perpendicular transitions. The K-type equidistant rotational spacings of 11.1(2) cm-1 (NH4+) and 29(3) cm-1 (H2O) deviate systematically from the corresponding values of the free molecules, a fact which is rationalized in terms of a symmetric top analysis. The relative band intensities recorded compare favorably with predictions of high level ab initio calculations, except on the nu3(H2O) band for which the observed value is about 20 times weaker than the calculated one. The nu3(H2O)/nu1(H2O) intensity ratios from other published action spectra in other cationic complexes vary such that the nu3(H2O) intensities become smaller the stronger the complexes are bound. The recorded ratios vary, in particular, among the data collected from action spectra that were recorded with and without rare gas tagging. The calculated anharmonic coupling constants in NH4+(H2O) further suggest that the coupling of the nu3(H2O) and nu1(H2O) modes to other cluster modes indeed varies by orders of magnitude. These findings together render a picture of a mode specific fragmentation dynamic that modulates band intensities in action spectra with respect to absorption spectra. Additional high level electronic structure calculations at the coupled-cluster singles and doubles with a perturbative treatment of triple excitations [CCSD(T)] level of theory with large basis sets allow for the determination of an accurate binding energy and enthalpy of the NH4+(H2O) cluster. The authors' extrapolated values at the CCSD(T) complete basis set limit are De [NH4+-(H2O)]=-85.40(+/-0.24) kJ/mol and DeltaH(298 K) [NH4+-(H2O)]=-78.3(+/-0.3) kJ/mol (CC2), in which double standard deviations are indicated in parentheses.     

Ab initio molecular orbital study of structures and energetics of Si(3)H(2), Si(3)H(2) (+), and Si(3)H(2) (-)

The geometric structures, isomeric stabilities, and potential energy profiles of various isomers and transition states in Si(3)H(2) neutral, cation and anion are investigated at the coupled-cluster singles, doubles (triples) level of theory. For the geometrical survey, the basis sets used are of the Dunning's correlation consistent basis sets of triple-zeta quality (cc-pVTZ) for the neutral and cation and the Dunning's correlation consistent basis sets of double-zeta quality with diffuse functions (aug-cc-pVDZ) for the anion. For the final energy calculations, the aug-cc-pVTZ: Dunning's correlation consistent basis sets of triple-zeta quality with diffuse functions and cc-pVQZ: Dunning's correlation consistent basis sets of quadruple-zeta quality basis sets are used for the neutral and the aug-cc-pVTZ ones for the cation and anion. The global minimum neutral (I-1: (1)A(1)) has the same framework as that (cyclopropenylidene) of the C(3)H(2) molecule. Other low-lying three isomers (I-2, I-3, and I-4) are also predicted to be within 20 kJ/mol. Five transition states are optimized and their energy relationships with the isomers are clarified. The geometric structure of the global minimum cation (C-1: (2)A(1)) has the same framework as that of the neutral, but that of the anion (A-1: (2)A(')) differs very much from those of the neutral and cation. The calculated vertical and adiabatic ionization potentials from the global minimum neutral (I-1) are 7.85 and 7.77 eV, respectively. The adiabatic electron affinity of the neutral I-1 and the electron detachment energy of the global minimum anion (A-1) are predicted to be 1.21 and 1.92 eV, respectively. The two-electron three-centered bond is widely observed in the present Si(3)H(2) neutral, cation, and anion. The contour plots of their localized molecular orbitals clearly show the existence of such nonclassical chemical bonds.     

Accurate computational determination of the binding energy of the SO3 x H2O complex

Reliable thermochemical data for the reaction SO3 + H2O<-->SO3 x H2O (1a) are of crucial importance for an adequate modeling of the homogeneous H2SO4 formation in the atmosphere. We report on high-level quantum chemical calculations to predict the binding energy of the SO3 x H2O complex. The electronic binding energy is accurately computed to De = 40.9+/-1.0 kJ/mol = 9.8+/-0.2 kcal/mol. By using harmonic frequencies from density functional theory calculations (B3LYP/cc-pVTZ and TPSS/def2-TZVP), zero-point and thermal energies were calculated. From these data, we estimate D0 = -Delta H(1a)0(0 K) = 7.7+/-0.5 kcal/mol and Delta H(1a)0(298 K) = -8.3+/-1.0 kcal/mol.     

Structures and heats of formation of the neutral and ionic PNO, NOP, and NPO systems from electronic structure calculations

High level ab initio electronic structure calculations using the coupled cluster CCSD(T) method with augmented correlation-consistent basis sets extrapolated to the complete basis set limit have been performed on the PNO, NOP, and NPO isomers and their corresponding anions and cations. Geometries for all species were optimized up through the aug-cc-pV(Q+d)Z level and vibrational frequencies were calculated with the aug-cc-pV(T+d)Z basis set. The most stable of the three isomers is NPO and it is predicted to have a heat of formation of 23.3 kcal/mol. PNO is predicted to be only 1.7 kcal/mol higher in energy. The calculated adiabatic ionization potential of NPO is 12.07 eV and the calculated adiabatic electron affinity is 2.34 eV. The calculated adiabatic ionization potential of PNO is 10.27 eV and the calculated adiabatic electron affinity is only 0.24 eV. NOP is predicted to be much higher in energy by 29.9 kcal/mol. The calculated rotational constants for PNO and NPO should allow for these species to be spectroscopically distinguished. The adiabatic bond dissociation energies for the P[Single Bond]N, P[Single Bond]O, and N[Single Bond]O bonds in NPO and PNO are the same within approximately 10 kcal/mol and fall in the range of 72-83 kcal/mol.     

Threshold-photoelectron spectroscopic study of methyl-substituted hydrazine compounds

The valence shell electronic structures of methylhydrazine (CH(3)NHNH(2)), 1,1-dimethylhydrazine ((CH(3))(2)NNH(2)) and tetramethylhydrazine ((CH(3))(4)N(2)) have been studied by recording threshold and conventional (kinetic energy resolved) photoelectron spectra. Ab initio calculations have been performed on ammonia and the three methyl substituted hydrazines, with the structures being optimized at the B3-LYP/6-31+G(d) level of theory. The ionization energies of the valence molecular orbitals were calculated using the Green's function method, allowing the photoelectron bands to be assigned to specific molecular orbitals. The ground-state adiabatic and vertical ionization energies, as determined from the threshold photoelectron spectra, were IE(a) = 8.02 +/- 0.16 eV and IE(v) = 9.36 +/- 0.02 eV for methylhydrazine, IE(a) = 7.78 +/- 0.16 eV and IE(v) = 8.86 +/- 0.01 eV for 1,1-dimethylhydrazine and IE(a) = 7.26 +/- 0.16 eV and IE(v) = 8.38 +/- 0.01 eV for tetramethylhydrazine. Due to the large geometry change that occurs upon ionization, these IE(a) values are all higher than the true thresholds. New features have been observed in the inner valence region and these have been compared with similar structure in the spectrum of hydrazine. The effect of resonant autoionization on the threshold photoelectron yield is discussed. New heats of formation (Delta(f)H) are proposed for the three hydrazines on the basis of G3 calculations: 107, 94, and 95 kJ/mol for methylhydrazine, 1,1-dimethyhydrazine and tetramethylhydrazine, respectively. The previously reported Delta(f)H for tetramethylhydrazine is shown to be erroneous.     

Energy-resolved photoionization of alkylperoxy radicals and the stability of their cations

The photoionization of alkylperoxy radicals has been investigated using a newly developed experimental apparatus that combines the tunability of the vacuum ultraviolet radiation of the Advanced Light Source at Lawrence Berkeley National Laboratory with time-resolved mass spectrometry. Methylperoxy (CH(3)OO) and ethylperoxy (C(2)H(5)OO) radicals are produced by the reaction of pulsed, photolytically produced alkyl radicals with molecular oxygen, and the mass spectrum of the reacting mixture is monitored in time by using synchrotron-photoionization with a double-focusing mass spectrometer. The kinetics of product formation is used to confirm the origins and assignments of ionized species. The photoionization efficiency curve for CH(3)OO has been measured, and an adiabatic ionization energy of (10.33 +/- 0.05) eV was determined with the aid of Franck-Condon spectral simulations, including ionization to the lowest triplet and singlet cation states. Using the appearance energy of CH(3)(+) from CH(3)OO, an enthalpy of formation for CH(3)OO of Delta(f) (CH(3)OO) = (22.4 +/- 5) kJ mol(-1) is derived. The enthalpy of formation of CH(3)OO(+) is derived as Delta(f) = (1019 +/- 7) kJ mol(-1) and the CH(3)(+)-OO bond energy as (CH(3)(+) - O(2)) = (80 +/- 7) kJ mol(-1). The C(2)H(5)OO(+) signal is not detectable; however, the time profile of the ethyl cation signal suggests its formation from dissociative ionization of C(2)H(5)OO. Electronic structure calculations suggest that hyperconjugation reduces the stability of the ethylperoxy cation, making the C(2)H(5)OO(+) ground state only slightly bound with respect to the ground-state products, C(2)H(5)(+) and O(2). The value of the measured appearance energy of C(2)H(5)(+) is consistent with dissociative ionization of C(2)H(5)OO via the Franck-Condon favored ionization to the ? (1)A' state of C(2)H(5)OO(+).     

Gas-phase oxidation reactions of Ta2+: synthesis and properties of TaO(2+) and TaO2(2+)

Gas-phase reactions of Ta(2+) and TaO(2+) with oxidants, including thermodynamically facile O-atom donor N(2)O and ineffective donor CO, as well as intermediate donors C(2)H(4)O (ethylene oxide), H(2)O, O(2), CO(2), NO, and CH(2)O, were studied by Fourier transform ion cyclotron resonance mass spectrometry. All oxidants reacted with Ta(2+) by electron transfer yielding Ta(+), in accord with the high second ionization energy of Ta (ca. 16 eV). TaO(2+) was also produced with N(2)O, H(2)O, O(2), and CO(2), oxidants with ionization energies above 12 eV; CO reacted only by electron transfer. The following charge separation products were also observed: TaN(+) and TaO(+) with N(2)O; and TaO(+) with O(2), CO(2), and CH(2)O. TaOH(2+), formed with H(2)O, reacted with a second H(2)O by proton transfer. TaO(2+) abstracted an electron from N(2)O, H(2)O, O(2), CO(2), and CO. Oxidation of TaO(2+) by N(2)O was also observed to produce TaO(2)(2+); on the basis of density functional theory (DFT) results, this species is a dioxide, {O-Ta-O}(2+). TaO(2)(2+) reacted by electron transfer with N(2)O, CO(2), and CO to give TaO(2)(+). Additionally, it was found that TaO(2)(2+) oxidizes CO to CO(2) and that it acts as a catalyst in the oxidation of CO by N(2)O. TaO(2)(2+) also activates H(2) to form TaO(2)H(2+). On the basis of the rates of electron transfer from N(2)O, CO(2), and CO to Ta(2+), TaO(2+), and TaO(2)(2+), the following estimates were made for the second ionization energies of Ta, TaO, and TaO(2): IE[Ta(+)] = 15.8 ± 0.3 eV, IE[TaO(+)] = 16.0 ± 0.5 eV, and IE[TaO(2)(+)] = 16.9 ± 0.4 eV. These IEs, together with recently reported bond dissociation energies, D[Ta(+)-O] and D[OTa(+)-O], result in the following bond energies: D[Ta(2+)-O] = 657 ± 58 kJ mol(-1) and D[OTa(2+)-O] = 500 ± 63 kJ mol(-1), the first of which is in good agreement with the value obtained by DFT.     

Experimental and quantum-chemical studies on photoionization and dissociative photoionization of CH2Br2

The dissociative photoionization of CH2Br2 in a region approximately 10-24 eV was investigated with photoionization mass spectroscopy using a synchrotron radiation source. An adiabatic ionization energy of 10.25 eV determined for CH2Br2 agrees satisfactorily with predictions of 10.26 and 10.25 eV with G2 and G3 methods, respectively. Observed major fragment ions CH2Br+, CHBr+, and CBr+ show appearance energies at 11.22, 12.59, and 15.42 eV, respectively; minor fragment ions CHBr2+, Br+, and CH2+ appear at 12.64, 15.31, and 16.80 eV, respectively. Energies for formation of observed fragment ions and their neutral counterparts upon ionization of CH2Br2 are computed with G2 and G3 methods. Dissociative photoionization channels associated with six observed fragment ions are proposed based on comparison of determined appearance energies and predicted energies. An upper limit of DeltaH0f,298(CHBr+) < or = 300.7 +/- 1.5 kcal mol(-1) is derived experimentally; the adiabatic ionization energy of CHBr is thus derived to be < or = 9.17 +/- 0.23 eV. Literature values for DeltaH0f,298(CBr+) = 362.5 kcal mol(-1) and ionization energy of 10.43 eV for CBr are revised to be less than 332 kcal mol(-1) and 9.11 eV, respectively. Also based on a new experimental ionization energy, DeltaH0f,298(CH2Br2+) is revised to be 236.4 +/- 1.5 kcal mol(-1).     

CH2Cl与OH自由基反应机理的理论研究

The reaction mechanism of CH2Cl radical with OH radical to produce HCCl+H2O,HCOCl+H2 and H2CO+HCl has been studied by using quantum chemistry ab initio calculations. The optimized geometrical parameters,and vibrational frequencies of all species were obtained at the UMP2（FC）level of theory in conjunction with 6-311++G* basis set. Besides,the zero-point energies（ZPE）,relative energies and total energies of all species were calculated using Gaussian-3（G3）model. The results of theoretical study indicate that the activated intermediate CH2ClOH is first formed through a barrierless process,followed by atoms migration,radical groups rotation and bonds fission to produce HCCl+H2O,HCOCl+H2 and H2CO+HCl,respectively. And all channels are exothermic by 72.81,338.54 and 354.08 kJ/mol. The reaction heat of reactants to H2CO+HCl is 281.27 kJ/mol more than that of reactants to HCCl+H2O. This result accords with that of experiments.     

Photoionization of 1-alkenylperoxy and alkylperoxy radicals and a general rule for the stability of their cations

The photoionization of 1-alkenylperoxy radicals, which are peroxy radicals where the OO moiety is bonded to an sp2-hybridized carbon, is studied by experimental and computational methods and compared to the similar alkylperoxy systems. Quantum chemical calculations are presented for the ionization energy and cation stability of several alkenylperoxy radicals. Experimental measurements of 1-cyclopentenylperoxy (1-c-C5H7OO) and propargylperoxy (CH2=C=CHOO) photoionization are presented as examples. These radicals are produced by reaction of an excess of O2 with pulsed-photolytically produced alkenyl radicals. The kinetic behavior of the products confirms the formation of the alkenylperoxy radicals. Electronic structure calculations are employed to give structural parameters and energetics that are used in a Franck-Condon (FC) spectral simulation of the photoionization efficiency (PIE) curves. The calculations also serve to identify the isomeric species probed by the experiment. Adiabatic ionization energies (AIEs) of 1-c-C5H7OO (8.70 +/- 0.05 eV) and CH2=C=CHOO (9.32 +/- 0.05 eV) are derived from fits to the experimental PIE curves. From the fitted FC simulation superimposed on the experimental PIE curves, the splitting between the ground state singlet and excited triplet cation electronic states is also derived for 1-c-C5H7OO (0.76 +/- 0.05 eV) and CH2=C=CHOO (0.80 +/- 0.15 eV). The combination of the AIE(CH2=C=CHOO) and the propargyl heat of formation provides Delta f H(0)(o) (CH2=C=CHOO+) of (1162 +/- 8) kJ mol-1. From Delta f H(0)(o) (CH2=C=CHOO+) and Delta f H (0)(o) (C3H3+) it is also possible to extract the bond energy D(0)(o)(C3H3+-OO) of 19 kJ mol-1 (0.20 eV). Finally, from consideration of the relevant molecular orbitals, the ionization behavior of alkyl- and alkenylperoxy radicals can be generalized with a simple rule: Alkylperoxy radicals dissociatively ionize, with the exception of methylperoxy, whereas alkenylperoxy radicals have stable singlet ground electronic state cations.     

Ab initio study of the structure, bonding, vibrational spectra, and energetics of XBS+ (where X=H, F, and Cl)

High level ab initio electronic structure calculations at the CCSD(T) level with augmented correlation-consistent basis set extrapolated to complete basis set limit have been performed on XBS and XBS+ for X=H, F, and Cl. The geometries have been optimized up through the aug-cc-pV5Z level and the vibrational frequencies have been calculated with the aug-cc-pVQZ basis sets. Analysis of the bonding in XBS and XBS+ using natural bond orbital analysis shows that the BS bond in XBS is a triple bond, while in XBS+ it is a double bond. The energetic properties of XBS cation and its first excited state are reported. The calculated adiabatic ionization potential is 11.11+/-0.01 eV as compared to the experimental value of 11.11+/-0.03 eV for HBS. The adiabatic ionization potentials for FBS and CIBS are 10.89+/-0.01 and 10.57+/-0.01 eV, respectively.     

Simple <Emphasis Type="Italic">b</Emphasis> ions have cyclic oxazolone structures. A neutralization-reionization mass spectrometric and computational study of oxazolone radicals

The 2-methyloxazol-5-on-2-yl radical (3) and its deuterium labeled analogs were generated in the gas-phase by femtosecond electron-transfer and studied by neutralization-reionization mass spectrometry and quantum chemical calculations. Radical 3 undergoes fast dissociation by ring opening and elimination of CO and CH(3)CO. Loss of hydrogen is less abundant and involves hydrogen atoms from both the ring and side-chain positions. The experimental results are corroborated by the analysis of the potential energy surface of the ground electronic state in 3 using density functional, perturbational, and coupled-cluster theories up to CCSD(T) and extrapolated to the 6-311 ++ G(3df,2p) basis set. RRKM calculations of radical dissociations gave branching ratios for loss of CO and H that were k(CO)/k(H) > 10 over an 80-300 kJ mol(-1) range of internal energies. The driving force for the dissociations of 3 is provided by large Franck-Condon effects on vertical neutralization and possibly from involvement of excited electronic states. Calculations also provided the adiabatic ionization energy of 3, IE(adiab) = 5.48 eV and vertical recombination energy of cation 3(+), RE(vert) = 4.70 eV. The present results strongly indicate that oxazolone structures can explain fragmentations of b-type peptide ions upon electron capture, contrary to previous speculations.     

A theoretical and computational study of the anion, neutral, and cation Cu(H(2)O) complexes

An ab initio investigation of the potential energy surfaces and vibrational energies and wave functions of the anion, neutral, and cation Cu(H(2)O) complexes is presented. The equilibrium geometries and harmonic frequencies of the three charge states of Cu(H(2)O) are calculated at the MP2 level of theory. CCSD(T) calculations predict a vertical electron detachment energy for the anion complex of 1.65 eV and a vertical ionization potential for the neutral complex of 6.27 eV. Potential energy surfaces are calculated for the three charge states of the copper-water complexes. These potential energy surfaces are used in variational calculations of the vibrational wave functions and energies and from these, the dissociation energies D(0) of the anion, neutral, and cation charge states of Cu(H(2)O) are predicted to be 0.39, 0.16, and 1.74 eV, respectively. In addition, the vertical excitation energies, that correspond to the 4 (2)P<--4 (2)S transition of the copper atom, and ionization potentials of the neutral Cu(H(2)O) are calculated over a range of Cu(H(2)O) configurations. In hydrogen-bonded, Cu-HOH configurations, the vertical excitation and ionization energies are blueshifted with respect to the corresponding values for atomic copper, and in Cu-OH(2) configurations where the copper atom is located near the oxygen end of water, both quantities are redshifted.     

Heats of formation of Co(CO)(2)NOPR(3), R = CH(3) and C(2)H(5), and its ionic fragments

A joint threshold photoelectron photoion coincidence spectrometry (TPEPICO) and collision-induced dissociation (CID) study on the thermochemistry of Co(CO)(2)NOPR(3), R = CH(3) (Me) and C(2)H(5) (Et), complexes is presented. Adiabatic ionization energies of 7.36 +/- 0.04 and 7.24 +/- 0.04 eV, respectively, were extracted from scans of the total ion and threshold electron signals. In the TPEPICO study, the following 0 K onsets were determined for the various fragment ions: CoCONOPMe(3)(+), 8.30 +/- 0.05 eV; CoNOPMe(3)(+), 9.11 +/- 0.05 eV; CoPMe(3)(+) 10.80 +/- 0.05 eV; CoCONOPEt(3)(+), 8.14 +/- 0.05 eV; CoNOPEt(3)(+), 8.92 +/- 0.05 eV; and CoPEt(3)(+), 10.66 +/- 0.05 eV. These onsets were combined with the Co(+)-PR(3) (R = CH(3) and C(2)H(5)) bond dissociation energies of 2.88 +/- 0.11 and 3.51 +/- 0.17 eV, obtained from the TCID experiments, to derive the heats of formation of the neutral and ionic species. Thus, the Co(CO)(2)NOPR(3) (R = CH(3) and C(2)H(5)) 0 K heats of formation were found to be -350 +/- 13 and -376 +/- 18 kJ x mol(-)(1), respectively. These heats of formation were combined with the published heat of formation of Co(CO)(3)NO to determine the substitution enthalpies of the carbonyl to phosphine substitution reactions. Room-temperature values of the heats of formation are also given using the calculated harmonic vibrational frequencies. Analysis of the TCID experimental results provides indirectly the adiabatic ionization energies of the free phosphine ligands, P(CH(3))(3) and P(C(2)H(5))(3), of 7.83 +/- 0.03 and 7.50 +/- 0.03 eV, respectively.     

Combined vacuum ultraviolet laser and synchrotron pulsed field ionization study of CH2BrCl

The pulsed field ionization-photoelectron (PFI-PE) spectrum of bromochloromethane (CH2BrCl) in the region of 85,320-88,200 cm-1 has been measured using vacuum ultraviolet laser. The vibrational structure resolved in the PFI-PE spectrum was assigned based on ab initio quantum chemical calculations and Franck-Condon factor predictions. At energies 0-1400 cm-1 above the adiabatic ionization energy (IE) of CH2BrCl, the Br-C-Cl bending vibration progression (nu1+=0-8) of CH2BrCl+ is well resolved and constitutes the major structure in the PFI-PE spectrum, whereas the spectrum at energies 1400-2600 cm-1 above the IE(CH2BrCl) is found to exhibit complex vibrational features, suggesting perturbation by the low lying excited CH2BrCl+(A 2A") state. The assignment of the PFI-PE vibrational bands gives the IE(CH2BrCl)=85,612.4+/-2.0 cm-1 (10.6146+/-0.0003 eV) and the bending frequencies nu1+(a1')=209.7+/-2.0 cm-1 for CH2BrCl+(X2A'). We have also examined the dissociative photoionization process, CH2BrCl+hnu-->CH2Cl++Br+e-, in the energy range of 11.36-11.57 eV using the synchrotron based PFI-PE-photoion coincidence method, yielding the 0 K threshold or appearance energy AE(CH2Cl+)=11.509+/-0.002 eV. Combining the 0 K AE(CH2Cl+) and IE(CH2BrCl) values obtained in this study, together with the known IE(CH2Cl), we have determined the 0 K bond dissociation energies (D0) for CH2Cl+-Br (0.894+/-0.002 eV) and CH2Cl-Br (2.76+/-0.01 eV). We have also performed CCSD(T, full)/complete basis set (CBS) calculations with high-level corrections for the predictions of the IE(CH2BrCl), AE(CH2Cl+), IE(CH2Cl), D0(CH2Cl+-Br), and D0(CH2Cl-Br). The comparison between the theoretical predictions and experimental determinations indicates that the CCSD(T, full)/CBS calculations with high-level corrections are highly reliable with estimated error limits of <17 meV.     

Effect of metal ions (Li+, Na+, K+, Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+) and water coordination on the structure of glycine and zwitterionic glycine

Interactions between metal ions and amino acids are common both in solution and in the gas phase. Here, the effect of metal ions and water on the structure of glycine is examined. The effect of metal ions (Li+, Na+, K+, Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+) and water on structures of Gly.Mn+(H2O)m and GlyZwitt.Mn+(H2O)m (m = 0, 2, 5) complexes have been determined theoretically by employing the hybrid B3LYP exchange-correlation functional and using extended basis sets. Selected calculations were carried out also by means of CBS-QB3 model chemistry. The interaction enthalpies, entropies, and Gibbs energies of eight complexes Gly.Mn+ (Mn+ = Li+, Na+, K+, Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+) were determined at the B3LYP density functional level of theory. The computed Gibbs energies DeltaG degrees are negative and span a rather broad energy interval (from -90 to -1100 kJ mol(-1)), meaning that the ions studied form strong complexes. The largest interaction Gibbs energy (-1076 kJ mol(-1)) was computed for the NiGly2+ complex. Calculations of the molecular structure and relative stability of the Gly.Mn+(H2O)m and GlyZwitt.Mn+(H2O)m (Mn+ = Li+, Na+, K+, Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+; m = 0, 2, and 5) systems indicate that in the complexes with monovalent metal cations the most stable species are the NO coordinated metal cations in non-zwitterionic glycine. Divalent cations Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+ prefer coordination via the OO bifurcated bonds of the zwitterionic glycine. Stepwise addition of two and five water molecules leads to considerable changes in the relative stability of the hydrated species. Addition of two water molecules at the metal ion in both Gly.Mn+ and GlyZwitt.Mn+ complexes reduces the relative stability of metallic complexes of glycine. For Mn+ = Li+ or Na+, the addition of five water molecules does not change the relative order of stability. In the Gly.K+ complex, the solvation shell of water molecules around K+ ion has, because of the larger size of the potassium cation, a different structure with a reduced number of hydrogen-bonded contacts. This results in a net preference (by 10.3 kJ mol(-1)) of the GlyZwitt.K+H2O5 system. Addition of five water molecules to the glycine complexes containing divalent cations Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+ results in a net preference for non-zwitterionic glycine species. The computed relative Gibbs energies are quite high (-10 to -38 kJ mol(-1)), and the NO coordination is preferred in the Gly.Mn+(H2O)5 (Mn+ = Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+) complexes over the OO coordination.     

Photoelectron spectroscopy and thermochemistry of tert-butylisocyanide-substituted cobalt tricarbonyl nitrosyl

A new organometallic complex, Co(CO)2NOtBuNC, was synthesized and investigated by photoelectron spectroscopy (PES) and threshold photoelectron photoion coincidence (TPEPICO) spectrometry in order to determine its ionization energy as well as the bond energies in the ionic forms. The assignment of the nine peaks in the PES was based on Kohn-Sham molecular orbital energies, and an adiabatic ionization energy of 7.30 +/- 0.05 eV was determined. In the TPEPICO experiment, the following 0 K onsets were determined for the various fragment ions: CoCONOtBuNC+ (8.17 +/- 0.05 eV); CoNOtBuNC+ (9.01 +/- 0.05 eV); and CotBuNC+ (10.42 +/- 0.05 eV). Because the photon source did not extend above 14 eV, we could not observe the bare Co+ ion in the experiment. The heat of formation of the CotBuNC+ ion was estimated by ab initio and DFT calculations of the CoL+ + tBuNC --> CotBuNC+ + L (L = CO, NO, NH3, H2O, PMe3) substitution enthalpies.     

Accurate measurement of the relative bond energies of CO and H2O ligands in Fe+ mono- and bis-ligated complexes

The systems Fe(H(2)O)(n) (+)/CO[bond]H(2)O and Fe(CO)(n) (+)/CO[bond]H(2)O (n = 1 and 2) were investigated in a triple cell Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. Using mixtures of CO with a very small amount of water, the ligand exchange equilibrium was reached, allowing experimental determination of the relevant equilibrium constants and free energies of reaction. Quantum chemical calculations at the B3LYP level of theory on the reactant and product species allowed us to determine the entropic terms and to derive the relative bond energies of CO and H(2)O in the mono- and bis-ligated complexes. For n = 1, H(2)O is more strongly bound to Fe(+) than CO by 4.1 +/- 1.6 kJ x mol(-1) at 298 K. For n = 2, at the same temperature, H(2)O is more strongly bound than CO to (H(2)O)Fe(+) by 7.6 +/- 1.6 kJ x mol(-1), and to (CO)Fe(+) by more than 20.1 kJ x mol(-1).