The vibrational predissociation spectra of the H5O2 +RGn(RG = Ar,Ne) clusters: correlation of the solvent perturbations in the free OH and shared proton transitions of the Zundel ion

Predissociation spectra of the H(5)O(2) (+)RG(n)(RG = Ar,Ne) cluster ions are reported in energy regions corresponding to both the OH stretching (3350-3850 cm(-1)) and shared proton (850-1950 cm(-1)) vibrations. The two free OH stretching bands displayed by the Ne complex are quite close to the band origins identified earlier in bare H(5)O(2) (+) [L. I. Yeh, M. Okumura, J. D. Myers, J. M. Price, and Y. T. Lee, J. Chem. Phys. 91, 7319 (1989)], indicating that the symmetrical H(5)O(2) (+) "Zundel" ion remains largely intact in H(5)O(2) (+)Ne. The low-energy spectrum of the Ne complex is simpler than that observed previously for H(5)O(2) (+)Ar, and is dominated by two sharp transitions at 928 and 1047 cm(-1), with a weaker feature at 1763 cm(-1). The H(5)O(2) (+)Ar(n),n = 1-5 spectra generally exhibit complex band structures reflecting solvent-induced symmetry breaking of the Zundel core ion. The extent of solvent perturbation is evaluated with electronic structure calculations, which predict that the rare gas atoms should attach to the spectator OH groups of H(5)O(2) (+) rather than to the shared proton. In the asymmetric complexes, the shared proton resides closer to the more heavily solvated water molecule, leading to redshifts in the rare gas atom-solvated OH stretches and to blueshifts in the shared proton vibrations. The experimental spectra are compared with recent full-dimensional vibrational calculations (diffusion Monte Carlo and multimode/vibrational configuration interaction) on H(5)O(2) (+). These results are consistent with assignment of the strong low-energy bands in the H(5)O(2) (+)Ne spectrum to the vibration of the shared proton mostly along the O-O axis, with the 1763 cm(-1) band traced primarily to the out-of-phase, intramolecular bending vibrations of the two water molecules.     

Explicitly correlated coupled cluster calculations for the propargyl cation (H2C3H+) and related species

The vibrations of the propargyl cation (H(3)C(3)H(+)) have been studied by vibrational configuration interaction (VCI) calculations, using explicitly correlated coupled cluster theory at the CCSD(T*)-F12a level to determine the underlying 12-dimensional potential energy surface. The wavenumbers of the fundamental vibrations are predicted with an accuracy of ca. 5 cm(-1). Harmonic wavenumber shifts for three different energy minima of the complex H(2)C(3)H(+)·Ar are combined with the corresponding VCI values in order to provide a comparison with recent infrared photodissociation (IRPD) spectra (A. M. Ricks et al., J. Chem. Phys., 2010, 132, 051101). An excellent agreement between experiment and theory is obtained for bands ν(2) (symm. CH stretch), ν(3) (pseudoantisymm. CC stretch), and ν(4) (CH(2) scissoring). However, reassignments are suggested for the bands observed at 3238 cm(-1), the "doublets" around 3093 and 1111 cm(-1), and the band at 3182 cm(-1). The assignment of the latter to the asymmetric CH stretching vibration of c-C(3)H·Ar is certainly wrong; the combination tone ν(3) + ν(5) of H(2)C(3)H(+)·Ar is a more likely candidate. Furthermore, accurate proton affinities are predicted for the carbenes H(2)C(n) with n = 3-8, thereby providing data of interest for interstellar cloud chemistry.     

An IR study of (CO2)(+)n (n=3-8) cluster ions in the 1000-3800 cm-1 region

Infrared photodissociation (IRPD) spectra of carbon dioxide cluster ions, (CO(2))(n) (+) with n=3-8, are measured in the 1000-3800 cm(-1) region. IR bands assignable to solvent CO(2) molecules are observed at positions close to the vibrational frequencies of neutral CO(2) [1290 and 1400 cm(-1) (nu(1) and 2nu(2)), 2350 cm(-1) (nu(3)), and 3610 and 3713 cm(-1) (nu(1)+nu(3) and 2nu(2)+nu(3))]. The ion core in (CO(2))(n) (+) shows several IR bands in the 1200-1350, 2100-2200, and 3250-3500 cm(-1) regions. On the basis of previous IR studies in solid Ne and quantum chemical calculations, these bands are ascribed to the C(2)O(4) (+) ion, which has a semicovalent bond between the CO(2) components. The number of the bands and the bandwidth of the IRPD spectra drastically change with an increase in the cluster size up to n=6, which is ascribed to the symmetry change of (CO(2))(n) (+) by the solvation of CO(2) molecules and a full occupation of the first solvation shell at n=6.     

Infrared spectroscopy of Li(+)(CH4)1Ar(n), n = 1-6, clusters

Infrared predissociation (IRPD) spectra of Li(+)(CH(4))(1)Ar(n), n = 1-6, clusters are reported in the C-H stretching region from 2800 to 3100 cm(-1). The Li(+) electric field perturbs CH(4) lifting its tetrahedral symmetry and gives rise to multiple IR active modes. The observed bands arise from the totally symmetric vibrational mode, v(1), and the triple degenerate vibrational mode, v(3). Each band is shifted to lower frequency relative to the unperturbed CH(4) values. As the number of argon atoms is increased, the C-H red shift becomes less pronounced until the bands are essentially unchanged from n = 5 to n = 6. For n = 6, additional vibrational features were observed which suggested the presence of an additional conformer. By monitoring different photodissociation loss channels (loss of three Ar or loss of CH(4)), one conformer was uniquely associated with the CH(4) loss channel, with two bands at 2914 and 3017 cm(-1), values nearly identical to the neutral CH(4) gas-phase v(1) and v(3) frequencies. With supporting ab initio calculations, the two conformers were identified, both with a first solvent shell size of six. The major conformer had CH(4) in the first shell, while the conformer exclusively present in the CH(4) loss channel had six argons in the first shell and CH(4) in the second shell. This conformer is +11.89 kJ/mol higher in energy than the minimum energy conformer at the MP2/aug-cc-pVDZ level. B3LYP/6-31+G* level vibrational frequencies and MP2/aug-cc-pVDZ level single-point binding energies, D(e) (kJ/mol), are reported to support the interpretation of the experimental data.     

Vibrational mode frequencies of silica species in SiO2-H2O liquids and glasses from ab initio molecular dynamics

Vibrational spectroscopy techniques are commonly used to probe the atomic-scale structure of silica species in aqueous solution and hydrous silica glasses. However, unequivocal assignment of individual spectroscopic features to specific vibrational modes is challenging. In this contribution, we establish a connection between experimentally observed vibrational bands and ab initio molecular dynamics (MD) of silica species in solution and in hydrous silica glass. Using the mode-projection approach, we decompose the vibrations of silica species into subspectra resulting from several fundamental structural subunits: The SiO(4) tetrahedron of symmetry T(d), the bridging oxygen (BO) Si-O-Si of symmetry C(2v), the geminal oxygen O-Si-O of symmetry C(2v), the individual Si-OH stretching, and the specific ethane-like symmetric stretching contribution of the H(6)Si(2)O(7) dimer. This allows us to study relevant vibrations of these subunits in any degree of polymerization, from the Q(0) monomer up to the fully polymerized Q(4) tetrahedra. Demonstrating the potential of this approach for supplementing the interpretation of experimental spectra, we compare the calculated frequencies to those extracted from experimental Raman spectra of hydrous silica glasses and silica species in aqueous solution. We discuss observed features such as the double-peaked contribution of the Q(2) tetrahedral symmetric stretch, the individual Si-OH stretching vibrations, the origin of the experimentally observed band at 970 cm(-1) and the ethane-like vibrational contribution of the H(6)Si(2)O(7) dimer at 870 cm(-1).     

Infrared photodissociation spectroscopy of protonated acetylene and its clusters

The protonated acetylene cation, C2H3+, (also known as the vinyl cation) and the proton-bound acetylene dimer cation (C4H5+) are produced by a pulsed supersonic nozzle/pulsed electrical discharge cluster source. The parent ions are also generated with weakly attached argon "tag" atoms, e.g., C2H3+Ar and C4H5+Ar. These ions are mass selected in a specially designed reflectron time-of-flight mass spectrometer and studied with infrared laser photodissociation spectroscopy in the 800-3600 cm-1 region. Vibrational resonances are detected for both ions in the C-H stretching region. C2H3+ has a strong vibrational resonance near 2200 cm-1 assigned to the bridged proton stretch of the nonclassical ion, while C4H5+ has no such free-proton vibration. Instead, C4H5+ has resonances near 1300 cm-1, consistent with a symmetrically shared proton in a di-bridged structure. Although the shared proton structure is not the lowest energy isomer of C4H5+, this species is apparently stabilized under the supersonic beam conditions. Larger clusters containing additional acetylene units are also investigated via the elimination of acetylene. These species have new IR bands indicating that rearrangement reactions have taken place to produce core C4H5+ ions with the methyl cyclopropane cation structure and/or the protonated cyclobutadiene isomer. Ab initio (MP2) calculations provide structures and predicted spectra consistent with all of these experiments.     

Infrared photodissociation spectroscopy of V+(CO2)n and V+(CO2)nAr complexes

V+(CO2)n and V+(CO2)nAr complexes are generated by laser vaporization in a pulsed supersonic expansion. The complexes are mass-selected within a reflectron time-of-flight mass spectrometer and studied by infrared resonance-enhanced (IR-REPD) photodissociation spectroscopy. Photofragmentation proceeds exclusively through loss of intact CO2 molecules from V+(CO2)n complexes or by elimination of Ar from V+(CO2)nAr mixed complexes. Vibrational resonances are identified and assigned in the region of the asymmetric stretch of free CO2 at 2349 cm(-1). A linear geometry is confirmed for V+(CO2). Small complexes have resonances that are blueshifted from the asymmetric stretch of free CO2, consistent with structures in which all ligands are bound directly to the metal ion. Fragmentation of the larger clusters terminates at the size of n=4, and a new vibrational band at 2350 cm(-1) assigned to external ligands is observed for V+(CO2)5 and larger cluster sizes. These combined observations indicate that the coordination number for CO2 molecules around V+ is exactly four. Fourfold coordination contrasts with that seen in condensed phase complexes, where a coordination number of six is typical for V+. The spectra of larger complexes provide evidence for an intracluster insertion reaction that produces a metal oxide-carbonyl species.     

Spectroscopic identification of the CO-H2O 2-1 cluster trapped in an argon matrix

The infrared spectra of the carbon monoxide-water cluster as well as the CO monomer and dimer in an argon matrix at cryogenic temperatures have been reinvestigated on the basis of the isotope substitution experiment with 12CO and 13CO. Lines due to the CO-H2O 2-1 cluster in the matrix have been unambiguously identified in the CO and OH stretching regions. The isotope effect on the vibrational frequency of the cluster is observed in the CO stretching vibration but neither in the symmetric nor antisymmetric OH stretching vibrations. Each of the two vibrational lines due to the two CO vibrations of the CO-H2O 2-1 cluster is examined by comparing the expected spectral features at a 12CO/13CO ratio on a simulation with those observed experimentally. The migration of the trapped molecules (CO and H2O) in the matrix is discussed, in which the observed spectral change with the deposition temperature from 14 K to 30 K is explained.     

Vibrational spectroscopy of Ni+ (benzene)n complexes in the gas phase

Ni+ (benzene)n (n = 1-6) and Ni+ (benzene)n Ar(1,2) (n = 1,2) are produced by laser vaporization in a pulsed nozzle cluster source. The clusters are mass selected and studied by infrared laser photodissociation spectroscopy in a reflectron time-of-flight mass spectrometer. The excitation laser is an OPO/OPA system that produces tunable IR in the C-H stretching region of benzene. Photodissociation of Ni+ (benzene)n complexes occurs by the elimination of intact neutral benzene molecules, while Ni+ (benzene)n Ar(1,2) complexes lose Ar. This process is enhanced on resonances, and the vibrational spectrum is obtained by monitoring the fragment yield versus the infrared wavelength. Vibrational bands in the 2700-3300 cm(-1) region are characteristic of the benzene molecular moiety with systematic shifts caused by the metal bonding. A dramatic change in the IR spectrum is seen at n = 3 and is attributed to the presence of external benzene molecules acting as solvent molecules in the cluster. The results of previous theoretical calculations are employed to investigate the structures, energetics, and vibrational frequencies of these complexes. The mono-benzene complex is found to have a C2v structure, with benzene distorted by the metal pi-bonding. The di-benzene complex is found to have a D2h structure, with both benzenes distorted. The comparison between experiment and theory provides intriguing new insight into the bonding in these prototypical pi-bonded organometallic complexes.     

The structure of protonated acetone and its dimer: infrared photodissociation spectroscopy from 800 to 4,000 cm-1

The infrared spectra of protonated acetone and the proton bound acetone dimer are obtained revealing vibrational resonances associated with the shared proton motions, which are in agreement with the predictions from ab initio, MP2, harmonic frequency calculations.     

Coherent low-frequency motions of hydrogen bonded acetic acid dimers in the liquid phase

Ultrafast vibrational dynamics of cyclic hydrogen bonded dimers and the underlying microscopic interactions are studied in temporally and spectrally resolved pump-probe experiments with 100 fs time resolution. Femtosecond excitation of the O-H and/or O-D stretching mode gives rise to pronounced changes of the O-H/O-D stretching absorption displaying both rate-like kinetic and oscillatory components. A lifetime of 200 fs is measured for the v=1 state of the O-H stretching oscillator. The strong oscillatory absorption changes are due to impulsively driven coherent wave packet motions along several low-frequency modes of the dimer between 50 and 170 cm(-1). Such wave packets generated via coherent excitation of the high-frequency O-H/O-D stretching oscillators represent a clear manifestation of the anharmonic coupling of low- and high-frequency modes. The underdamped low-frequency motions dephase on a time scale of 1-2 ps. Calculations of the vibrational potential energy surface based on density functional theory give the frequencies, anharmonic couplings, and microscopic elongations of the low-frequency modes, among them intermolecular hydrogen bond vibrations. Oscillations due to the excitonic coupling between the two O-H or O-D stretching oscillators are absent as is independently confirmed by experiments on mixed dimers with uncoupled O-H and O-D stretching oscillators.     

Vibrationally induced proton transfer in F- (H2O) and F- (D2O)

Vibrational predissociation spectra of the F(-)(H(2)O) x Ar and F(-)(D(2)O) x Ar complexes are observed over a range of 600 to 3800 cm(-1), which include bands attributed to the fundamentals as well as the first two overtones of the vibrations primarily associated with the shared hydrogen. This information allows us to characterize both the extended potential surface confining the anionic H-bonded hydrogen and the degree to which this motion is coupled to the motions of other atoms in the complex. We analyze these new data with reduced dimensional treatments using explicit potential energy and electric dipole moment surfaces. The often employed one-dimensional treatment with fixed OF distance does not even qualitatively account for the observed isotope dependent level structures, but a simple extension to two dimensions, corresponding to the OF distance and the shared proton position, accurately recovers the observed spectra. The resulting two-dimensional wave functions are used to evaluate the extent of proton transfer in each vibrational level. The main conclusion of this work is that vibrational excitation of the shared proton can be regarded as optically driven, intracluster proton transfer.     

IR plus vacuum ultraviolet spectroscopy of neutral and ionic organic acid molecules and clusters: acetic acid

Infrared (IR) vibrational spectroscopy of acetic acid (A) neutral and ionic monomers and clusters, employing vacuum ultraviolet (VUV), 10.5 eV single photon ionization of supersonically expanded and cooled acetic acid samples, is presented and discussed. Molecular and cluster species are identified by time of flight mass spectroscopy: the major mass features observed are A(n)H(+) (n=1-9), ACOOH(+) (VUV ionization) without IR radiation present, and A(+) with both IR and VUV radiation present. The intense feature ACOOH(+) arises from the cleavage of (A)(2) at the beta-CC bond to generate ACOOH(+)+CH(3) following ionization. The vibrational spectrum of monomeric acetic acid (2500-7500 cm(-1)) is measured by nonresonant ionization detected infrared (NRID-IR) spectroscopy. The fundamentals and overtones of the CH and OH stretches and some combination bands are identified in the spectrum. Mass selected IR spectra of neutral and cationic acetic acid clusters are measured in the 2500-3800 cm(-1) range employing nonresonant ionization dip-IR and IR photodissociation (IRPD) spectroscopies, respectively. Characteristic bands observed at approximately 2500-2900 cm(-1) for the cyclic ring dimer are identified and tentatively assigned. For large neutral acetic acid clusters A(n)(n>2), spectra display only hydrogen bonded OH stretch features, while the CH modes (2500-2900 cm(-1)) do not change with cluster size n. The IRPD spectra of protonated (cationic) acetic acid clusters A(n)H(+) (n=1-7) exhibit a blueshift of the free OH stretch with increasing n. These bands finally disappear for n> or =6, and one broad and weak band due to hydrogen bonded OH stretch vibrations at approximately 3350 cm(-1) is detected. These results indicate that at least one OH group is not involved in the hydrogen bonding network for the smaller (n< or =5) A(n)H(+) species. The disappearance of the free OH stretch feature at n> or =6 suggests that closed cyclic structures form for A(n)H(+) for the larger clusters (n> or =6).     

Structures of [(CO2)n(CH3OH)m](-) (n = 1-4, m = 1, 2) cluster anions

The infrared photodissociation spectra of [(CO 2) n (CH 3OH) m ] (-) ( n = 1-4, m = 1, 2) are measured in the 2700-3700 cm (-1) range. The observed spectra consist of an intense broad band characteristic of hydrogen-bonded OH stretching vibrations at approximately 3300 cm (-1) and congested vibrational bands around 2900 cm (-1). No photofragment signal is observed for [(CO 2) 1,2(CH 3OH) 1] (-) in the spectral range studied. Ab initio calculations are performed at the MP2/6-311++G** level to obtain structural information such as optimized structures, stabilization energies, and vibrational frequencies of [(CO 2) n (CH 3OH) m ] (-). Comparison between the experimental and the theoretical results reveals the structural properties of [(CO 2) n (CH 3OH) m ] (-): (1) the incorporated CH 3OH interacts directly with either CO 2 (-) or C 2O 4 (-) core by forming an O-HO linkage; (2) the introduction of CH 3OH promotes charge localization in the clusters via the hydrogen-bond formation, resulting in the predominance of CO 2 (-).(CH 3OH) m (CO 2) n-1 isomeric forms over C 2O 4 (-).(CH 3OH) m (CO 2) n-2 ; (3) the hydroxyl group of CH 3OH provides an additional solvation cite for neutral CO 2 molecules.     

Iterative solutions with energy selected bases for highly excited vibrations of tetra-atomic molecules

The use of energy selected bases (ESB) with iterative diagonalization of the Hamiltonian matrix is described for vibrations of tetra-atomic systems. The performance of the method is tested by computing vibrational states of HOOH below 10,000 cm(-1) (1296 A+ symmetry states) and H(2)CO below 13,500 cm(-1) (729 A(1) symmetry states). For iterative solutions, we tested both the implicitly restarted Lanczos method (IRLM) and the standard (nonreorthogonalizing) Lanczos approach. Comparison with other contracted basis approach as well as direct product grid representation shows superior performance of the ESB/IRLM approach. Of the two systems, H(2)CO is found to be more challenging than HOOH since it has much stronger couplings among vibrational modes, which leads to a drastically larger primitive basis set. For H(2)CO we also discuss some interesting behavior of the molecule in the high internal energy regime.     

Vibrationally resolved photoionization dynamics of CF4 in the D 2A1 state

Vibrationally resolved photoelectron spectroscopy of the CF4+ (D 2A1) state is studied for the first time over an extended energy range, 26.5相似文献   

Vibrational spectroscopy of nitroalkane chains using electron autodetachment and ar predissociation

If the binding energy of an excess electron is lower than some of the vibrational levels of its host anion, vibrational excitation can lead to autodetachment. We use excitation of CH stretching modes in nitroalkane anions (2700-3000 cm(-1)), where the excess electron is localized predominantly on the NO2 group. We present data on nitroalkane anions of various chain lengths, showing that this technique is a valid approach to the vibrational spectroscopy of such systems extending to nitroalkane anions at least the size of nitropentane. We compare spectra taken by using vibrational autodetachment with spectra obtained by monitoring Ar evaporation from Ar solvated nitroalkane anions. The spectra of nitromethane and nitroethane are assigned on the basis of ab initio calculations with a detailed analysis of Fermi resonances of CH stretching fundamentals with overtones and combination bands of HCH bending modes.     

A combined theoretical and experimental study of the reaction products of laser-ablated thorium atoms with CO: first identification of the CThO, CThO(-), OthCCO, OTh(eta(3)-CCO), and Th(CO)(n) (n = 1-6) molecules

Laser-ablated thorium atoms have been reacted with CO molecules during condensation in excess neon. Absorptions at 617.7 and 812.2 cm(-1) are assigned to Th-C and Th-O stretching vibrations of the CThO molecule. Absorptions at 2048.6, 1353.6, and 822.5 cm(-1) are assigned to the OThCCO molecule, which is formed by CO addition to CThO and photochemical rearrangement of Th(CO)(2). The OThCCO molecule undergoes further photoinduced rearrangement to OTh(eta(3)-CCO), which is characterized by C-C, C-O, and Th-O stretching vibrations at 1810.8, 1139.2, and 831.6 cm(-1). The Th(CO)(n) (n = 1-6) complexes are formed on deposition or on annealing. Evidence is also presented for the CThO(-) and Th(CO)(2)(-) anions, which are formed by electron capture of neutral molecules. Relativistic density functional theory (DFT) calculations of the geometry structures, vibrational frequencies, and infrared intensities strongly support the experimental assignments. It is found that CThO is an unprecedented actinide-containing carbene molecule with a triplet ground state and an unusual bent structure ( angleCThO = 109 degrees ). The OThCCO molecule has a bent structure while its rearranged product OTh(eta(3)-CCO) is found to have a unique exocyclic structure with side-bonded CCO group. We also find that both Th(CO)(2) and Th(CO)(2)(-) are, surprisingly, highly bent, with the angleC-Th-C bond angle being close to 50 degrees; the unusual geometries are the result of extremely strong Th-to-CO back-bonding, which causes significant three-centered bonding among the Th atom and the two C atoms.     

Reactions of laser-ablated zinc and cadmium atoms with CO: infrared spectra of the Zn(CO)x (x = 1-3), CdCO-, and Cd(CO)2 molecules in solid neon

Reactions of laser-ablated zinc and cadmium atoms with carbon monoxide molecules in solid neon have been investigated using matrix-isolation infrared spectroscopy. Based on the isotopic substitution, absorptions at 1852.2, 1901.9, 1945.9, and 1995.2 cm(-1) are assigned to the C-O stretching vibrations of the ZnCO, Zn(CO)(2), and Zn(CO)(3) molecules. Absorptions at 1735.8, 1961.3, and 2035.7 cm(-1) are assigned to the C-O stretching vibrations of the CdCO(-) and Cd(CO)(2) molecules. In contrast with the previous argon experiments, more species and more valuable information about the reaction of zinc and cadmium atoms with CO have been obtained in solid neon. Density functional theory calculations have been performed on these zinc and cadmium carbonyls. The agreement between the experimental and calculated vibrational frequencies, relative absorption intensities, and isotopic shifts substantiates the identification of these carbonyls from the matrix infrared spectrum. The present experiments also reveal that zinc is more reactive with CO than cadmium.