Enols of amides. The effect of fluorine substituents in the ester groups of dicarboalkoxyanilidomethanes on the enol/amide and E-enol/Z-enol ratios. A multinuclei NMR study.

Condensation of phenyl isocyanate substituted by 4-MeO, 4-Me, 4-H, 4-Br, and 2,4-(MeO)(2) with esters CH(2)(CO(2)R)CO(2)R', R = CH(2)CF(3), R' = CH(3), CH(2)CF(3), CH(CF(3))(2), or R = CH(3), R' = CH(CF(3))(2) gave 17 "amides" ArNHCOCH(CO(2)R)CO(2)R' containing three, six, or nine fluorines in the ester groups. X-ray crystallography of six of them revealed that compounds with > or =6 fluorine atoms exist in the solid state as the enols of amides ArNHC(OH)=C(CO(2)R)CO(2)R' whereas the ester with R = R' = CH(3) was shown previously to have the amide structure. In the solid enols, the OH is cis and hydrogen bonded to the better electron-donating (i.e., with fewer fluorine atoms) ester group. X-ray diffraction could not be obtained for compounds with only three fluorine atoms, i.e., R = CH(2)CF(3), R' = CH(3) but the (13)C CP-MAS spectra indicate that they have the amide structure in the solid state, whereas esters with six and nine fluorine atoms display spectra assigned to the enols. The solid enols show unsymmetrical hydrogen bonds and the expected features of push-pull alkenes, e.g., long C(alpha)=C(beta) bonds. The structure in solution depends on the number of fluorine atoms and the solvent, but only slightly on the substituents. The symmetrical systems (R = R' = CH(2)CF(3)) show signals for the amide and the enol, but all systems with R not equal R' displayed signals for the amide and for two enols, presumably the E- and Z-isomers. The [Enol I]/[Enol II] ratio is 1.6-2.9 when R = CH(2)CF(3), R' = CH(3), CH(CF(3))(2) and 4.5-5.3 when R = CH(3), R' = CH(CF(3))(2). The most abundant enol display a lower field delta(OH) and a higher field delta(NH) and assigned the E-structure with a stronger O-H.O=C(OR) hydrogen bond than in the Z-isomer. delta(OH) and delta(NH) values are nearly the same for all systems with the same cis CO(2)R group. The [Enols]/[Amide] ratio in various solvents follows the order CCl(4) > CDCl(3) > CD(3)CN > DMSO-d(6). The enols always predominate in CCl(4) and the amide is the exclusive isomer in DMSO-d(6) and the major one in CD(3)CN. In CDCl(3) the major tautomer depends on the number of fluorines. For example, in CDCl(3,) for Ar = Ph, the % enol (K(Enol)) is 35% (0.54) for R = CH(2)CF(3,) R' = CH(3), 87% (6.7) for R = R' = CH(2)CF(3), 79% (3.8) for R = CH(3), R' = CH(CF(3))(2) and 100% (> or =50) for R = CH(2)CF(3), R' = CH(CF(3))(2). (17)O and (15)N NMR spectra measured for nine of the enols are consistent with the suggested assignments. The data indicate the importance of electron withdrawal at C(beta), of intramolecular hydrogen bonding, and of low polarity solvents in stabilizing the enols. The enols of amides should no longer be regarded as esoteric species.     

High-resolution ESR study of the H...CH3, H...CHD2, D...CH2D, and D...CD3 radical pairs in solid argon

High-resolution electron spin resonance (ESR) spectra of radical pairs of a hydrogen atom that coupled with a methyl radical (H...CH3, H...CHD2, D...CH2D, and D...CD3) were observed for X-ray irradiated solid argon containing selectively deuterium-labeled methanes, CH4, CH2D2, and CD4, at 4.2 K. The double-quartet 1H-hyperfine (hf) splittings of ca. 26 and 1.16 mT at the Deltam(s) = +/-1 and Deltam(s) = +/-2 transitions, which are one-half of the isotropic 1H-hf splittings of an isolated H-atom and a CH3 radical, were attributed to the H...CH3 pair. The 1H-hf splittings at the Deltam(s) = +/-1 transition were further split by the fine structure (fs) due to the electron dipole-dipole coupling. Because of the high-resolution spectra, three different sets of the fs splitting, d, are clearly resolved in the spectra of both the H...CH3 and the D...CD3 pairs. The separation distance (inter-spin distance), R, between the H-atom and the CH3 radical being in pairs was evaluated from the d values based on a point-dipole interaction model. For the case of the H...CH3 pair, the observed d values of 4.2, 4.9, and 5.1 mT yield the respective separations, R = 0.87, 0.83, and 0.82 nm, to probe the trapping site of the pair in an Ar crystalline lattice (fcc). For the pair with R = 0.87 nm, for example, we propose that the CH3 radical occupies a substitutional site and the counter H-atom occupies either the interstitial tetrahedral sites directed away from the CH3 radicals by a distance of 0.87 nm or the interstitial octahedral sites by a distance of 0.88 nm. When a mixture of CH4 and CD4 in a solid Ar matrix was irradiated, only two different radical pairs, H...CH3 and D...CD3, were observed. This result clearly demonstrates that the hydrogen atom and methyl radicals, which undergo a pairwise trapping, can originate from the same methane molecule.     

Experimental and theoretical study of the carbon-13 and deuterium kinetic isotope effects in the Cl and OH reactions of CH3F

A laser flash photolysis-resonance fluorescence technique has been employed to determine absolute rate coefficients for the CH3F + Cl reaction in N2 bath gas in the temperature range of 200-700 K and pressure range of 33-133 hPa. The data were fitted to a modified Arrhenius expression k(T) = 1.14 x 10(-12) x (T/298)2.26 exp{-313/T}. The OH and Cl reaction rates of (13)CH3F and CD3F have been measured by long-path FTIR spectroscopy relative to CH3F at 298 +/- 2 K and 1013 +/- 10 hPa in purified air. The FTIR spectra were fitted using a nonlinear least-squares spectral fitting method including line data from the HITRAN database and measured infrared spectra as references. The relative reaction rates defined by alpha = k(light)/k(heavy) were determined to be k(OH+CH3F)/k(OH+CD3F) = 4.067 +/- 0.018, k(OH+CH3F)/k(OH+(13)CH3F) = 1.067 +/- 0.006, k(Cl+CH3F)/k(Cl+CD3F) = 5.11 +/- 0.07, and k(Cl+CH3F)/k(Cl+(13)CH3F) = 1.016 +/- 0.006. The carbon-13 and deuterium kinetic isotope effects in the OH and Cl reactions of CH3F have been further investigated by quantum chemistry methods and variational transition state theory.     

High-resolution slice imaging of quantum state-to-state photodissociation of methyl bromide

The photodissociation of rotationally state-selected methyl bromide is studied in the wavelength region between 213 and 235 nm using slice imaging. A hexapole state selector is used to focus a single (JK=11) rotational quantum state of the parent molecule, and a high speed slice imaging detector measures directly the three-dimensional recoil distribution of the methyl fragment. Experiments were performed on both normal (CH(3)Br) and deuterated (CD(3)Br) parent molecules. The velocity distribution of the methyl fragment shows a rich structure, especially for the CD(3) photofragment, assigned to the formation of vibrationally excited methyl fragments in the nu(1) and nu(4) vibrational modes. The CH(3) fragment formed with ground state Br((2)P(3/2)) is observed to be rotationally more excited, by some 230-340 cm(-1), compared to the methyl fragment formed with spin-orbit excited Br((2)P(1/2)). Branching ratios and angular distributions are obtained for various methyl product states and they are observed to vary with photodissociation energy. The nonadiabatic transition probability for the (3)Q(0+)-->(1)Q(1) transition is calculated from the images and differences between the isotopes are observed. Comparison with previous non-state-selected experiments indicates an enhanced nonadiabatic transition probability for state-selected K=1 methyl bromide parent molecules. From the state-to-state photodissociation experiments the dissociationenergy for both isotopes was determined, D(0)(CH(3)Br)=23 400+/-133 cm(-1) and D(0)(CD(3)Br)=23 827+/-94 cm(-1).     

Stable enols of amides ArNHC(OH)=C(CN)CO(2)R. E/Z enols,equilibria with the amides,solvent effects,and hydrogen bonding

The structures of anilido cyano(fluoroalkoxycarbonyl)methanes ArNHCOCH(CN)CO(2)R, where R = CH(2)CF(3) or CH(CF(3))(2), Ar = p-XC(6)H(4), and X = MeO, Me, H, or Br, were investigated. In the solid state, all exist as the enols ArNHC(OH)=C(CN)CO(2)R 7 (R = CH(2)CF(3)) and 9 (R = CH(CF(3))(2)) with cis arrangement of the hydrogen-bonded ROC=O.HO moiety and a long C1=C2 bond. The product composition in solution is solvent dependent. In CDCl(3) solution, only a single enol is observed, whereas in THF-d(8) and CD(3)CN, two enols (E and Z) are the major products, and the amide is the minor product or not observed at all (K(Enol) 1.04-9 (CD(3)CN, 298 K) and 3 to >/=100 (THF, 300 K)). The percentage of the amide and the Z-enol increase upon an increase in temperature. In all solvents, the percent enol is higher for 9 than for 7. In CD(3)CN, more enol is observed when the aryl group is more electron-donating. The spectra in DMSO-d(6) and DMF-d(7) indicate the presence of mostly a single species, whose spectra do not change on addition of a base and is ascribed to the anion of the ionized carbon acid. Comparison with systems where the CN is replaced by a CO(2)R group (R = CH(2)CF(3), CH(CF(3))(2)) shows a higher percentage of enol for the CN-substituted system. Intramolecular (to CO(2)R) and intermolecular hydrogen bonds determine, to a significant extent, the stability of the enols, their Z/E ratios (e.g., Z/E (THF, 240 K) = 3.2-4.0 (7) and 0.9-1.3 (9)), and their delta(OH) in the (1)H spectra. The interconversion of Z- and E-enol by rotation around the C=C bond was studied by DNMR, and DeltaG() values of >/=15.3 and 14.1 +/- 0.4 kcal/mol for Z-7 and Z-9 were determined. Features of the NMR spectra of the enols and their anions are discussed.     

Effective rate constants for the surface reaction between solid methanol and deuterium atoms at 10 K

The surface reactions of CH3OH, CH2DOH, and CHD2OH with cold D atoms at 10 K were investigated using an atomic beam source and FTIR. Methyl-deuterated isotopologues CH2DOH, CHD2OH, and CD3OH were produced by exposure of amorphous solid CH3OH to D atoms at 10 K, and the pseudo-first-order rates for the reactions CH3OH + D --> CH2OH + HD, CH2DOH + D --> CHDOH + HD, and CHD2OH + D --> CD2OH + HD were estimated. The ratios of the reaction rates of the second and third reactions to the first reaction were 0.69 +/- 0.11 and 0.52 +/- 0.14, respectively. The difference in reaction rates is thought to be due to a secondary kinetic isotope effect on the H-abstraction reaction from the methyl side by D atoms.     

Microwave and ab initio studies of the Xe-CH4 van der Waals complex

An ab initio potential-energy surface of the Xe-CH4 van der Waals complex was constructed at the coupled cluster level of theory with single, double, and perturbatively included triple excitations. The recently developed small-core pseudopotential and augmented correlation-consistent polarized valence quadruple-zeta basis set was used for the xenon atom and Dunning's augmented correlation-consistent polarized valence triple-zeta basis set for the other atoms. The basis sets were supplemented with bond functions. Dipole moments were also calculated at various configurations. Rotational spectra of the Xe-CH4 van der Waals complex were recorded using a pulsed-nozzle Fourier transform microwave spectrometer. The isotopomers studied include those of CH4,13CH4,CD4,CH3D, and CHD3 with the five most abundant Xe isotopes. Transitions within three internal rotor states, namely, the j=0,K=0; j=1,K=0; and j=2,K=1 states, were observed and assigned. Nuclear quadrupole hyperfine structures due to the presence of 131Xe(I=3/2) were detected and analyzed. It was found that the j=1,K=0 state is perturbed by a Coriolis interaction with a nearby j=1,K=1 state. For isotopomers containing CH3D and CHD3, the j=2 states are no longer metastable and could not be observed. The spectroscopic results were used to derive structural and dynamical information of the Xe-CH4 complex.     

Deuteration effects on the structure and infrared spectrum of CH5(+)

The CH5+ molecular ion is well-known for its large amplitude motions that lead to complete scrambling of the hydrogen atoms, even in the vibrational ground state. Experiments have been reported that probe the consequences of these large amplitude motions. We recently reported that quantum zero-point effects partially quench the scrambling when CH5+ is partially deuterated. Here, the consequences of this quantum localization are investigated through calculations of the low-resolution spectra of CH4D+, CHD4+, and CD5+. The spectra are obtained by convoluting stick spectra, evaluated for individual stationary points on an ab initio potential surface, multiplying them by Diffusion Monte Carlo ground state density at that stationary point, and taking the sum. The CH/D stretch regions of CH4D+ and CD5+ are red-shifted relative to CH5+, while the overall shape of the envelope remains unaffected. In contrast, for CHD4+, the shape of the spectral envelope in the CH/D stretch region differs from the other three isotopologs. These signatures of the quantum localization of the deuterium on the spectra are discussed.     

New linear tricobalt complex of di(2-pyridyl)amide (dpa), [Co3(dpa)4(CH3CN)2][PF6]2

Reaction of the linear tricobalt compound Co3(dpa)4Cl2 (1) (dpa = di(2-pyridyl)amide) with silver hexafluorophosphate in acetonitrile yields [Co3(dpa)4(CH3CN)2][PF6]2 (2). Two crystalline forms are obtained from the same solution, namely, a monoclinic (P2(1)) form 2xCH3CNx2Et2O and a triclinic (P1) form, 2x3CH3CN. The tricobalt units in both crystals are essentially symmetrical, though this is not required by crystal symmetry, with Co-Co distances in the range 2298-2304 A. Each of the two terminal Co atoms is coordinated to an acetonitrile molecule with Co-N distances in the range 2068-2111 A at 213 K. The spiral arrangement of ligands gives an overall idealized D4 point group symmetry for the cation [Co3(dpa)4(CH3CN)2]2+ . Chiral crystals of both delta and lambda configurations in the P2(1) form have been isolated. The absolute configurations were determined by X-ray crystallography and their mirror-image circular dichroism spectra measured. The D4 symmetry of the cation appears to be preserved in solution as judged by the presence of only five proton resonance signals in the 1H NMR spectrum. Magnetic susceptibility measurements in the solid state indicates that 2 has a doublet ground state and exhibits an increase of the effective moment at high temperature (approximately 160 K) due to a spin crossover process.     

Vibrational characterization of the tertiary amide and thioamide group

Force field calculations and vibrational spectra of (CH(3))(2)NCOCON(CH(3))(2) (TMO), (CH(3))(2)NCOCSN(CH(3))(2) (TMMTO) and (CH(3))(2)NCSCSN(CH(3))(2) (TMDTO) are discussed. The amide and thioamide fundamentals and those of other simple tertiary amides are compared. A characteristic pattern in infrared and Raman is proposed.     

13C, 18O, and D fractionation effects in the reactions of CH3OH isotopologues with Cl and OH radicals

A relative rate experiment is carried out for six isotopologues of methanol and their reactions with OH and Cl radicals. The reaction rates of CH2DOH, CHD2OH, CD3OH, (13)CH3OH, and CH3(18)OH with Cl and OH radicals are measured by long-path FTIR spectroscopy relative to CH3OH at 298 +/- 2 K and 1013 +/- 10 mbar. The OH source in the reaction chamber is photolysis of ozone to produce O((1)D) in the presence of a large excess of molecular hydrogen: O((1)D) + H2 --> OH + H. Cl is produced by the photolysis of Cl2. The FTIR spectra are fitted using a nonlinear least-squares spectral fitting method with measured high-resolution infrared spectra as references. The relative reaction rates defined as alpha = k(light)/k(heavy) are determined to be: k(OH + CH3OH)/k(OH + (13)CH3OH) = 1.031 +/- 0.020, k(OH + CH3OH)/k(OH + CH3(18)OH) = 1.017 +/- 0.012, k(OH + CH3OH)/k(OH + CH2DOH) = 1.119 +/- 0.045, k(OH + CH3OH)/k(OH + CHD2OH) = 1.326 +/- 0.021 and k(OH + CH3OH)/k(OH + CD3OH) = 2.566 +/- 0.042, k(Cl + CH3OH)/k(Cl + (13)CH3OH) = 1.055 +/- 0.016, k(Cl + CH3OH)/k(Cl + CH3(18)OH) = 1.025 +/- 0.022, k(Cl + CH3OH)/k(Cl + CH2DOH) = 1.162 +/- 0.022 and k(Cl + CH3OH)/k(Cl + CHD2OH) = 1.536 +/- 0.060, and k(Cl + CH3OH)/k(Cl + CD3OH) = 3.011 +/- 0.059. The errors represent 2sigma from the statistical analyses and do not include possible systematic errors. Ground-state potential energy hypersurfaces of the reactions were investigated in quantum chemistry calculations at the CCSD(T) level of theory with an extrapolated basis set. The (2)H, (13)C, and (18)O kinetic isotope effects of the OH and Cl reactions with CH3OH were further investigated using canonical variational transition state theory with small curvature tunneling and compared to experimental measurements as well as to those observed in CH4 and several other substituted methane species.     

Infrared spectrum of matrix isolated selenoformaldehyde, CH2Se, and CD2Se

Thermolysis of highly diluted (CH2Se)3 or (CD2Se)3 in a flow of argon with subsequent quenching of the products in an matrix at 15 K yields monomeric CH2Se and CD2Se, respectively. Six fundamental vibrations upsilon1 = 2972.5, upsilon2 = 1413.3, upsilon3 = 854.2, upsilon4 = 916.4, upsilon 5 = 3052.9, and upsilon 6 = 913.2 cm(-1) and two combination bands have been observed for CH2Se as well as three fundamentals of CD2Se. The vibrational wavenumbers are compared with those of CH2O and CH2S. Matrix isolated selenoformaldehyde decomposes slowly by UV photolysis to yield the CSe molecule.     

Infrared and Raman study of the fast internal motion of non-rigid molecules,method of selective deuteration

The internal rotation of the methyl group in toluene and nitromethane and the ring-puckering motion of cyclopentene have been studied by analysing the infrared and Raman spectra of the ν(CH) or ν(CD) stretching vibrations of the CH or CD oscillators isolated in selectively deuterated molecules.The interpretation of the spectra is supported by a general formalism of anharmonic coupling between the high-frequency and low-frequency modes. The latter is described in quantum mechanics in the gas and solid state but takes a stochastic character in the liquid state.     

Nuclear spin conversion of methane in solid parahydrogen

The nuclear spin conversion of CH(4) and CD(4) isolated in solid parahydrogen was investigated by high resolution Fourier transform infrared spectroscopy. From the analysis of the temporal changes of rovibrational absorption spectra, the nuclear spin conversion rates associated with the rotational relaxation from the J=1 state to the J=0 state for both species were determined at temperatures between 1 and 6 K. The conversion rate of CD(4) was found to be 2-100 times faster than that of CH(4) in this temperature range. The faster conversion in CD(4) is attributed to the quadrupole interaction of D atoms in CD(4), while the conversion in CH(4) takes place mainly through the nuclear spin-nuclear spin interaction. The conversion rates depend on crystal temperature strongly above 3.5 K for CH(4) and above 2 K for CD(4), while the rates were almost constant below these temperatures. The temperature dependence indicates that the one-phonon process is dominant at low temperatures, while two-phonon processes become important at higher temperatures as a cause of the nuclear spin conversion.     

Quasiclassical trajectory study of the C(1D) + H2 reaction and isotopomeric variants: kinetic isotope effect and CD/CH branching ratio

The recently proposed ab initio single-sheeted double many-body expansion potential energy for the methylene molecule has been used to perform quasiclassical trajectory (QCT) calculations for the title reaction. Thermal and initial state-specific (v = 0, j = 0) rate constants for the C((1)D) + H(2)/HD/D(2) reactions have been obtained over a wide range of temperatures. Cross sections for the reaction C((1)D) + H(2) and its deuterated isotopes have also been calculated, as well as the CD/CH branching ratios for the C((1)D) + HD reaction. It is found that the CD + H product channel in the C((1)D) + HD reaction is preferred relative to the CH + D channel. The estimated rate constants are predicted to be in the order k(H2) > k(HD) > k(D2) and the calculated cross sections and rate constants compared with available theoretical and experimental data.     

Dialkoxyphosphinyl-substituted enols of carboxamides

Reactions of isocyanates XNCO (e.g., X = p-An, Ph, i-Pr) with (MeO)2P(=O)CH2CO2R [R = Me, CF3CH2, (CF3)2CH] gave 15 formal "amides" (MeO)2P(=O)CH(CO2R)CONHX (6/7), and with (CF3CH2O)2P(=O)CH2CO2R [R = Me, CF3CH2] they gave eight analogous amide/enols 17/18. X-ray crystallography of two 6/7, R = (CF3)2CH systems revealed Z-enols of amides structures (MeO)2P(=O)C(CO2CH(CF3)2)=C(OH)NHX 7 where the OH is cis and hydrogen bonded to the O=P(OMe)2 group. The solid phosphonates with R = Me, CF3CH2 have the amide 6 structure. The structures in solution were investigated by 1H, 13C, 19F, and 31P NMR spectra. They depend strongly on the substituent R and the solvent and slightly on the N-substituent X. All systems displayed signals for the amide and the E- and Z-isomers. The low-field two delta(OH) and two delta(NH) values served as a probe for the stereochemistry of the enols. The lower field delta(OH) is not always that for the more abundant enol. The % enol, presented as K(enol), was determined by 1H, 19F, and 31P NMR spectra, increases according to the order for R, Me < CF3CH2 < (CF3)2CH, and decreases according to the order of solvents, CCl4 > CDCl3 approximately THF-d8 > CD3CN >DMSO-d6. In DMSO-d6, the product is mostly only the amide, but a few enols with fluorinated ester groups were observed. The Z-isomers are more stable for all the enols 7 with E/Z ratios of 0.31-0.75, 0.15-0.33, and 0.047-0.16 when R = Me, CF3CH2, and (CF3)2CH, respectively, and for compounds 18, R = Me, whereas the E-isomers are more stable than the Z-isomers. Comparison with systems where the O=P(OMe)2 is replaced by a CO2R shows mostly higher K(enol) values for the O=P(OMe)2-substituted systems. A linear correlation exists between delta(OH)[Z-enols] activated by two ester groups and delta(OH)[E-enols] activated by phosphonate and ester groups. Compounds (MeO)2P(=O)CH(CN)CONHX show 相似文献   

Vibrational spectra and structure of CH3Cl:H2O, CH3Cl:HDO, and CH3Cl:D2O complexes. IR matrix isolation and ab initio calculations

The infrared spectra of CH3Cl + H2O isolated in solid neon at low temperatures have been investigated. The CH3Cl + H2O system is remarkable because of its propensity to form CH3Cl:H2O and CH3Cl:(H2O)n (n > or = 2) complexes. We focus here on the CH3Cl:H2O species. Low concentration studies (0.01-0.5%) and subsequent annealing lead to formation of the 1:1 CH3Cl:H2O complex with O-H. . .Cl-C or O. . .H-C intermolecular hydrogen bonds. Vibrational modes of this complex have been detected. In addition, spectra of D2O + CH3Cl and HDO + CH3Cl have also been recorded. A detailed vibrational analysis of partially deuterated species shows that HDO is exclusively D bonded to CH3Cl. This is a consequence of the preference for HDO to form a deuterium bonding complex rather than a hydrogen bonding one.     

Cooperativity of hydrogen-bonded networks in 7-azaindole(CH3OH)n (n=2,3) clusters evidenced by IR-UV ion-dip spectroscopy and natural bond orbital analysis

IR-UV ion-dip spectra of the 7-azaindole (7AI)(CH(3)OH)(n) (n=1-3) clusters have been measured in the hydrogen-bonded NH and OH stretching regions to investigate the stable structures of 7AI(CH(3)OH)(n) (n=1-3) in the S(0) state and the cooperativity of the H-bonding interactions in the H-bonded networks. The comparison of the IR-UV ion-dip spectra with IR spectra obtained by quantum chemistry calculations shows that 7AI(CH(3)OH)(n) (n=1-3) have cyclic H-bonded structures, where the NH group and the heteroaromatic N atom of 7AI act as the proton donor and proton acceptor, respectively. The H-bonded OH stretch fundamental of 7AI(CH(3)OH)(2) is remarkably redshifted from the corresponding fundamental of (CH(3)OH)(2) by 286 cm(-1), which is an experimental manifestation of the cooperativity in H-bonding interaction. Similarly, two localized OH fundamentals of 7AI(CH(3)OH)(3) also exhibit large redshifts. The cooperativity of 7AI(CH(3)OH)(n) (n=2,3) is successfully explained by the donor-acceptor electron delocalization interactions between the lone-pair orbital in the proton acceptor and the antibonding orbital in the proton donor in natural bond orbital (NBO) analyses.     

Isotopic and internal CX3 (X = D,H) rotational motion effects in the Ba...FCX3 + h nu --> BaF + CX3 intracluster reactions

Photodepletion and action spectra of the laser-induced Ba...FCD3 fragmentation have been measured over the 16 075-16 380 cm(-1) range. The observed band and peak structures allowed us to estimate the vibrational and rotational structures of the excited complex at the transition state configuration. The relative reaction probability P(R)(E) for the intracluster Ba...FCD3 + h nu --> BaF + CD3 reaction has been determined over the cited energy range. P(R)(E) shows a peak structure with an energy spacing of 8.9 cm(-1) which was attributed to an internal rotation of the CD3 group in the intermediate state. A comparison with previous Ba...FCH3 photofragmentation spectra reveals the dynamical role of the internal CX3 (X = H,D) motion which is manifested by the presence of rotational resonances in the laser-induced intracluster reaction.     

Vibrational relaxation of CN stretch of pseudo-halide anions (OCN-, SCN-, and SeCN-) in polar solvents

The vibrational relaxation dynamics of pseudo-halide anions XCN- (X = O, S, Se) in polar solvents were studied to understand the effect of charge on solute-to-solvent intermolecular energy transfer (IET) and solvent assisted intramolecular vibrational relaxation (IVR) pathways. The T1 relaxation times of the CN stretch in these anions were measured by IR pump/IR probe spectroscopy, in which the 0-1 transition was excited, and the 0-1 and 1-2 transitions were monitored to follow the recovery of the ground state and decay of the excited state. For these anions in five solvents, H2O, D2O, CH3OH, CH3CN, and (CH3)2SO, relaxation rates followed the trend of OCN- > SCN- > SeCN-. For these anions and isotopes of SCN-, the relaxation rate was a factor of a few (2.5-10) higher in H2O than in D2O. To further probe the solvent isotope effect, the relaxation rates of S12C14N-, S13C14N-, and S12C15N- in deuterated methanols (CH3OH, CH3OD, CH3OH, CD3OD) were compared. Relaxation rate was found to be affected by the change of solvent vibrational band at the CN- stretching mode (CD3 symmetric stretch) and lower frequency regions, suggesting the presence of both direct IET and solvent assisted IVR relaxation pathways. The possible relaxation pathways and mechanisms for the observed trends in solute and solvent dependence were discussed.