Properties of the B+-H2 and B+-D2 complexes: a theoretical and spectroscopic study

The rotationally resolved infrared spectrum of the B+-D2 ion-neutral complex is recorded in the D-D stretch vibration region (2805–2875  cm−1) by detecting B+ photofragments. Analysis of the spectrum confirms a T-shaped equilibrium geometry for the B+-D2 complex with a vibrationally averaged intermolecular bond length of 2.247 Å, around 0.02 Å shorter than for the previously characterised B+-H2 complex [V. Dryza, B. L. J. Poad, and E. J. Bieske, J. Am. Chem. Soc. 130, 12986 (2008)10.1021/ja8018302]. The D-D stretch band centre occurs at 2839.76 ± 0.10 cm−1, representing a −153.8  cm−1 shift from the Q1(0) transition of the free D2 molecule. A new three dimensional ab initio potential energy surface for the B++H2 interaction is calculated using the coupled cluster RCCSD(T) method and is used in variational calculations for the rovibrational energies of B+-H2 and B+-D2. The calculations predict dissociation energies of 1254  cm−1 for B+-H2 with respect to the B++H2 (j = 0) limit, and 1313  cm−1 for B+-D2 with respect to the B++D2 (j = 0) limit. The theoretical approach reproduces the rotational and centrifugal constants of the B+-H2 and B+-D2 complexes to within 3%, and the magnitude of the contraction of the intermolecular bond accompanying excitation of the H2 or D2 sub-unit, but underestimates the H-H and D-D vibrational band shifts by 7%–8%. Combining the theoretical and experimental results allows a new, more accurate estimation for the B+-H2 band origin (3939.64 ± 0.10  cm−1)

Rotationally resolved infrared spectrum of the Li+_D2 cation complex

The infrared spectrum of mass selected Li +-D 2 cations is recorded in the D-D stretch region (2860-2950 cm -1) in a tandem mass spectrometer by monitoring Li + photofragments. The D-D stretch vibration of Li +-D 2 is shifted by -79 cm -1 from that of the free D 2 molecule indicating that the vibrational excitation of the D 2 subunit strengthens the effective Li +-D 2 intermolecular interaction. Around 100 rovibrational transitions, belonging to parallel K a=0-0, 1-1, and 2-2 subbands, are fitted to a Watson A-reduced Hamiltonian to yield effective molecular parameters. The infrared spectrum shows that the complex consists of a Li + ion attached to a slightly perturbed D 2 molecule with a T-shaped equilibrium configuration and a 2.035 A vibrationally averaged intermolecular separation. Comparisons are made between the spectroscopic data and data obtained from rovibrational calculations using a recent three dimensional Li +-D 2 potential energy surface [R. Martinazzo, G. Tantardini, E. Bodo, and F. Gianturco, J. Chem. Phys. 119, 11241 (2003)]

Zeitschrift für pädagogische Historiographie : ZpH

We describe recent experiments in which mass spectrometry and laser spectroscopy are combined to characterize Li(+)-H(2), Na(+)-H(2), B(+)-H(2) and Al(+)-H(2) complexes in the gas-phase. The infrared spectra, which feature full resolution of rotational sub-structures, are recorded by monitoring M(+) photofragments as the infrared wavelength is scanned. The spectra deliver detailed information on the way, in which a hydrogen molecule is attached to a metal cation including the intermolecular separation, the force constant for the intermolecular bond and the H-H stretching frequency. The complexes all possess T-shaped equilibrium geometries and display a clear correlation between the length and force constant of the intermolecular bond and the dissociation energy. In contrast, the data do not support any straightforward correlation between the frequency shift for the H-H stretch mode and the dissociation energy

Spectroscopic Study of the Benchmark Mn+-H-2 Complex

We have recorded the rotationally resolved infrared spectrum of the weakly bound Mn+-H-2, complex in the H-H stretch region (4022-4078 cm(-1)) by monitoring Mn+ photodissociation products. The band center of Mn+-H-2, the H-H stretch transition, is shifted by -111.8 cm(-1) from the transition of the free H-2 molecule. The spectroscopic data suguest that the Mn+-H-2 complex consists of a slightly perturbed H-2 molecule attached to the Mn+ ion in a T-shaped configuration with a vibrationally averaged intermolecular separation of 2.73 angstrom. Together with the measured Mn+center dot center dot center dot H-2 binding energy of 7.9 kJ/mol (Weis, P.; et al. J. Phys. Chem. A 1997, 101, 2809.), the spectroscopic parameters establish Mn+-H-2 as the most thoroughly characterized transition-metal cation-dihydrogen complex and a benchmark for calibrating quantum chemical calculations on noncovalent systems involving open d-shell configurations. Such systems are of possible importance for hydrogen storage applications

Infrared spectra of mass-selected Al+_(CH4)nN=1-6clusters

Infrared spectra are recorded for Al+–(CH4)n n = 1–6 clusters in the CH stretch region (2800–3100 cm−1). The spectra, which are obtained by monitoring photofragmentation in a tandem mass spectrometer, are dominated by a single, narrow band corresponding to the totally symmetric C–H stretching mode of the CH4 subunits (rendered infrared active through the interaction with the Al+ cation). This band shifts progressively to higher wavenumber as the clusters becomes larger, concomitant with a weakening of the intermolecular Al+⋯CH4 bonds. Supporting ab initio calculations for the n = 1–6 clusters at the MP2/aug-cc-pVDZ level indicate that the Al+ cation is attached to each CH4 sub-unit in a face-bound η3 configuration and that when possible the methane molecules are adjacent to one another. Clusters built around an inserted [H–Al–CH3]+ core are also predicted to be stable but lie higher in energy than clusters built around an Al+ core; the latter species are the only ones observed experimentally

Communication: New insight into the barrier governing CO2 formation from OH+CO

Despite its relative simplicity, the role of tunneling in the reaction OH + CO -> H + CO2 has eluded the quantitative predictive powers of theoretical reaction dynamics. In this study a one-dimensional effective barrier to the formation of H + CO2 from the HOCO intermediate is directly extracted from dissociative photodetachment experiments on HOCO and DOCO. Comparison of this barrier to a computed minimum-energy barrier shows that tunneling deviates significantly from the calculated minimum-energy pathway, predicting product internal energy distributions that match those found in the experiment and tunneling lifetimes short enough to contribute significantly to the overall reaction. This barrier can be of direct use in kinetic and statistical models and aid in the further refinement of the potential energy surface and reaction dynamics calculations for this system. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3589860

Ocean physics and engineering

The dissociative photodetachment of NO-(H2O) and NO-(CD4) anion clusters was studied at 775 nm (1.60 eV) using photoelectron-photofragment coincidence spectroscopy. The correlation between the photoelectron and photodetached neutral spectra indicates vibrational excitation in the recoiling NO neutral fragments from NO-(H2O), with a progression consistent with vibrational excitation up to v(NO) = 3 in the products. The correlation remains when D2O is substituted for H2O, implying the NO vibrational mode plays a role in the dissociation coordinate of the complex. In contrast, no correlation was observed between photoelectron kinetic energy and kinetic energy release from NO-(CD4). Consideration of the maximum available kinetic energy allows the binding energies to be detemined as 0.57 and 0.07 eV for NO-(H2O) and NO-(CD4), respectively

Infrared spectra of the Li +_(H 2)n(n=1-3) cation complexes

The Li+–(H2)n n = 1–3 complexes are investigated through infrared spectra recorded in the H–H stretch region (3980–4120 cm−1) and through ab initio calculations at the MP2∕aug-cc-pVQZ level. The rotationally resolved H–H stretch band of Li+–H2 is centered at 4053.4 cm−1 [a −108 cm−1 shift from the Q1(0) transition of H2]. The spectrum exhibits rotational substructure consistent with the complex possessing a T-shaped equilibrium geometry, with the Li+ ion attached to a slightly perturbed H2 molecule. Around 100 rovibrational transitions belonging to parallel Ka = 0‐0, 1-1, 2-2, and 3-3 subbands are observed. The Ka = 0‐0 and 1-1 transitions are fitted by a Watson A-reduced Hamiltonian yielding effective molecular parameters. The vibrationally averaged intermolecular separation in the ground vibrational state is estimated as 2.056 Å increasing by 0.004 Å when the H2 subunit is vibrationally excited. The spectroscopic data are compared to results from rovibrational calculations using recent three dimensional Li+–H2 potential energy surfaces [ Martinazzo et al., J. Chem. Phys. 119, 11241 (2003); Kraemer and Špirko, Chem. Phys. 330, 190 (2006) ]. The H–H stretch band of Li+–(H2)2, which is centered at 4055.5 cm−1 also exhibits resolved rovibrational structure. The spectroscopic data along with ab initio calculations support a H2–Li+–H2 geometry, in which the two H2 molecules are disposed on opposite sides of the central Li+ ion. The two equivalent Li+⋯H2 bonds have approximately the same length as the intermolecular bond in Li+–H2. The Li+–(H2)3 cluster is predicted to possess a trigonal structure in which a central Li+ ion is surrounded by three equivalent H2 molecules. Its infrared spectrum features a broad unresolved band centered at 4060 cm−1

Infrared spectra of mass-selected Al+-(CH4)(n) n=1-6 clusters

Infrared spectra are recorded for Al+-(CH4)n n = 1-6 clusters in the CH stretch region (2800-3100 cm(-1)). The spectra, which are obtained by monitoring photofragmentation in a tandem mass spectrometer, are dominated by a single, narrow band corresponding to the totally symmetric C-H stretching mode of the CH4 subunits (rendered infrared active through the interaction with the Al+ cation). This band shifts progressively to higher wavenumber as the clusters becomes larger, concomitant with a weakening of the intermolecular Al+center dot center dot center dot CH4 bonds. Supporting ab initio calculations for the n = 1-6 clusters at the MP2/aug-cc-pVDZ level indicate that the Al+ cation is attached to each CH4 sub-unit in a face-bound eta(3) configuration and that when possible the methane molecules are adjacent to one another. Clusters built around an inserted [H-Al-CH3](+) core are also predicted to be stable but lie higher in energy than clusters built around an Al+ core; the latter species are the only ones observed experimentally. Crown Copyright (C) 2008 Published by Elsevier B.V. All rights reserved