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7 Oct 2006

Volume 125, Issue 13, Articles (13xxxx)

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back to top Spectroscopy

The bending vibrational levels of the acetylene cation: A case study of the Renner-Teller effect in a molecule with two degenerate bending vibrations

Sheunn-Jiun Tang, Yung-Ching Chou, Jim Jr-Min Lin, and Yen-Chu Hsu

J. Chem. Phys. 125, 133201 (2006); http://dx.doi.org/10.1063/1.2199827 (15 pages) | Cited 10 times

Online Publication Date: 2 October 2006

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Forty three vibronic levels of C2H2+, math math, with υ4 = 0–6, υ5 = 0–3, and K = 0–4, lying at energies of 0–3520 cm−1 above the zero-point level, have been recorded at rotational resolution. These levels were observed by double resonance, using 1+1′ two-color pulsed-field ionization zero-kinetic-energy photoelectron spectroscopy. The intermediate states were single rovibrational levels chosen from the math math, 4ν3 (K = 1–2), 5ν3 (K = 1), ν2+4ν3 (K = 0), and 47 206 cm−1 (K = 1) levels of C2H2. Seven of the trans-bending levels of C2H2+ (υ4 = 0–3, K = 0–2) had been reported previously by Pratt et al. [ J. Chem. Phys. 99, 6233 (1993) ]; our results for these levels agree well with theirs. A full analysis has been carried out, including the Renner-Teller effect and the vibrational anharmonicity for both the trans- and cis-bending vibrations. The rotational structure of the lowest 16 vibronic levels (consisting of the complete set of levels with υ4+υ5 ⩽ 2, except for the unobserved upper math component of the 2ν4 overtone) could be fitted by least squares using 16 parameters to give an rms deviation of 0.21 cm−1. The vibronic coupling parameter ε5 (about whose magnitude there has been controversy) was determined to be −0.02737. For the higher vibronic levels, an additional parameter, r45, was needed to allow for the Darling-Dennison resonance between the two bending manifolds. Almost all the observed levels of the υ4+υ5 = 3 and 4 polyads (about half of the predicted number) could then be assigned. In a final fit to 39 vibronic levels with υ4+υ5 ⩽ 5, an rms deviation of 0.34 cm−1 was obtained using 20 parameters. An interesting finding is that Hund’s spin-coupling cases (a) and (b) both occur in the Σu components of the ν4+2ν5 combination level. The ionization potential of C2H2 (from the lowest rotational level of the ground state to the lowest rotational level of the cation) is found to be 91 953.77±0.09 cm−1 (3σ).
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33.20.Tp Vibrational analysis
33.20.Sn Rotational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.60.+q Photoelectron spectra
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy

Probing the electronic structure of UO+ with high-resolution photoelectron spectroscopy

Vasiliy Goncharov, Leonid A. Kaledin, and Michael C. Heaven

J. Chem. Phys. 125, 133202 (2006); http://dx.doi.org/10.1063/1.2213262 (8 pages) | Cited 14 times

Online Publication Date: 2 October 2006

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The pulsed field ionization–zero kinetic energy photoelectron technique has been used to observe the low-lying energy levels of UO+. Rotationally resolved spectra were recorded for the ground state and the first nine electronically excited states. Extensive vibrational progressions were characterized. Ω+ assignments were unambiguously determined from the first rotational lines identified in each vibronic band. Term energies, vibrational frequencies, and anharmonicity constants for low-lying energy levels of UO+ are reported. In addition, accurate values for the ionization energies for UO [48643.8(2) cm−1] and U [49957.6(2) cm−1] were determined. The pattern of low-lying electronic states for UO+ indicates that they originate from the U3+(5f3)O2− configuration, where the uranium ion-centered interactions between the 5f electrons are significantly stronger than interactions with the intramolecular electric field. The latter lifts the degeneracy of U3+ ion-core states, but the atomic angular momentum quantum numbers remain reasonably well defined.
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33.60.+q Photoelectron spectra
33.20.Sn Rotational analysis
33.20.Tp Vibrational analysis
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy

An empirical approach to the bond additivity model in quantitative interpretation of sum frequency generation vibrational spectra

Hui Wu, Wen-kai Zhang, Wei Gan, Zhi-feng Cui, and Hong-fei Wang

J. Chem. Phys. 125, 133203 (2006); http://dx.doi.org/10.1063/1.2352746 (12 pages) | Cited 9 times

Online Publication Date: 3 October 2006

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Knowledge of the ratios between different polarizability βi′j′k′ tensor elements of a chemical group in a molecule is crucial for quantitative interpretation and polarization analysis of its sum frequency generation vibrational spectroscopy (SFG-VS) spectrum at interface. The bond additivity model (BAM) or the hyperpolarizability derivative model along with experimentally obtained Raman depolarization ratios has been widely used to obtain such tensor ratios for the CH3, CH2, and CH groups. Successfully, such treatment can quantitatively reproduce the intensity polarization dependence in SFG-VS spectra for the symmetric (SS) and asymmetric (AS) stretching modes of CH3 and CH2 groups, respectively. However, the relative intensities between the SS and AS modes usually do not agree with each other within this model even for some of the simplest molecular systems, such as the air/methanol interface. This fact certainly has cast uncertainties on the effectiveness and conclusions based on the BAM. One of such examples is that the AS mode of CH3 group has never been observed in SFG-VS spectra from the air/methanol interface, while this AS mode is usually very strong for SFG-VS spectra from the air/ethanol interface, other short chain alcohol, as well as long chain surfactants. In order to answer these questions, an empirical approach from known Raman and IR spectra is used to make corrections to the BAM. With the corrected ratios between the βi′j′k′ tensor elements of the SS and AS modes, all features in the SFG-VS spectra of the air/methanol and air/ethanol interfaces can be quantitatively interpreted. This empirical approach not only provides new understandings of the effectiveness and limitations of the bond additivity model but also provides a practical way for its application in SFG-VS studies of molecular interfaces.
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68.03.Kn Dynamics (capillary waves)
68.03.Hj Liquid surface structure: measurements and simulations
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
63.50.-x Vibrational states in disordered systems
78.30.-j Infrared and Raman spectra

Gold as hydrogen: Structural and electronic properties and chemical bonding in Si3Au3+/0/− and comparisons to Si3H3+/0/−

Boggavarapu Kiran, Xi Li, Hua-Jin Zhai, and Lai-Sheng Wang

J. Chem. Phys. 125, 133204 (2006); http://dx.doi.org/10.1063/1.2216707 (7 pages) | Cited 19 times

Online Publication Date: 4 October 2006

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A single Au atom has been shown to behave like H in its bonding to Si in several mono- and disilicon gold clusters. In the current work, we investigate the Au/H analogy in trisilicon gold clusters, Si3Au3+/0/−. Photoelectron spectroscopy and density functional calculations are combined to examine the geometric and electronic structure of Si3Au3−. We find that there are three isomers competing for the ground state of Si3Au3− as is the case for Si3H3−. Extensive structural searches show that the potential energy surfaces of the trisilicon gold clusters (Si3Au3−, Si3Au3, and Si3Au3+) are similar to those of the corresponding silicon hydrides. The lowest energy isomers for Si3Au3− and Si3Au3 are structurally similar to a Si3Au four-membered ring serving as a common structural motif. For Si3Au3+, the 2π aromatic cyclotrisilenylium auride ion, analogous to the aromatic cyclotrisilenylium ion (Si3H3+), is the most stable species. Comparison of the structures and chemical bonding between Si3Au3+/0/− and the corresponding silicon hydrides further extends the isolobal analogy between Au and H.
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36.40.Mr Spectroscopy and geometrical structure of clusters
36.40.Cg Electronic and magnetic properties of clusters
33.60.+q Photoelectron spectra
31.15.E- Density-functional theory
31.50.Bc Potential energy surfaces for ground electronic states
33.15.Fm Bond strengths, dissociation energies

Decay dynamics of the long-range math math state of D2 and H2: Experiment and theory

Stephen C. Ross, Toshio Yoshinari, Yoshihiro Ogi, and Koichi Tsukiyama

J. Chem. Phys. 125, 133205 (2006); http://dx.doi.org/10.1063/1.2264331 (24 pages) | Cited 7 times

Online Publication Date: 5 October 2006

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We present accurate experimental measurements of the lifetimes of rovibrational levels of the long-range math math state for both D2 and H2, obtained directly from the observation of the time-dependent decay of the fluorescence from these excited levels. These results improve upon and extend those of Reinhold et al. [J. Chem. Phys. 112, 10754 (2000) ]. Several decay pathways are open to these levels including fluorescence, predissociation, and autoionization. We present theoretical results for each of these processes, each calculated using the simplest but still appropriate level of theory. In particular, the theoretical calculations provide a quantitative explanation of the dramatic vibrational dependence of the observed lifetimes, the isotope dependence of the lifetimes for levels well localized within the math potential well and therefore not subject to significant tunneling, and an insight into the role of enhanced tunneling in autoionization. In these calculations each of the rovibrational levels of the math state is treated individually, without having to engage in a global coupled-state calculation.
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33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
33.20.Vq Vibration-rotation analysis
33.50.Dq Fluorescence and phosphorescence spectra
33.80.Gj Diffuse spectra; predissociation, photodissociation
33.80.Eh Autoionization, photoionization, and photodetachment

The calculated infrared spectrum of Cl−H2O using a new full dimensional ab initio potential surface and dipole moment surface

Jaime Rheinecker and Joel M. Bowman

J. Chem. Phys. 125, 133206 (2006); http://dx.doi.org/10.1063/1.2209675 (10 pages) | Cited 8 times

Online Publication Date: 5 October 2006

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We report a full dimensional, ab initio-based global potential energy surface (PES) and dipole moment surface for Cl−H2O. Both surfaces are symmetric with respect to interchange of the H atoms. The PES is a fit to thousands of electronic energies calculated using the coupled-cluster method [CCSD(T)] with a moderately large basis (aug-cc-pVTZ). Vibrational energies and wave functions are accurately obtained using MULTIMODE. The wave function and dipole moment surface are used to calculate and analyze the pure infrared spectrum at 0 K which is compared with experiment. Vibrational energies and the infrared spectra for DOD and HOD/DOH are also presented.
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33.20.Ea Infrared spectra
31.15.A- Ab initio calculations
31.15.bw Coupled-cluster theory
31.50.-x Potential energy surfaces
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
36.40.Mr Spectroscopy and geometrical structure of clusters
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