A theoretical study on the ionization of OCS with an analysis of vibrational structures of the photoelectron spectrum

 Ab initio calculations have been performed to study the molecular structures and vibrational levels of the four low-lying ionic states (1, 2²Π, and 1, 2²Σ⁺) of carbonyl sulfide. The global regions of the potential-energy surfaces have been obtained by multireference single and double excitation configuration interaction calculations. Vibrational calculations using explicit vibrational Hamiltonians have been used for vibrational analysis. The equilibrium molecular structures and a vibrational analysis of the four ionic states are presented. The theoretical ionization intensity curves including the vibrational structures of the ionic states are also presented and are compared with the photoelectron spectrum. Received: 20 January 2001 / Accepted: 22 August 2001 / Published online: 30 October 2001     

A simulation of the photoelectron spectrum of pyrazolide

Building on previous theoretical and spectroscopic studies of the pyrazolyl radical, a new three-state quasidiabatic Hamiltonian is reported which reproduces not only the equilibrium geometries and harmonic frequencies of the nominal X (2)A(2) state and low-lying A (2)B(1) excited state, but also the minimum energy points on the lowest two-state (X (2)A(2), A (2)B(1)) and three-state (X (2)A(2), A (2)B(1), B (2)B(2)) seams of conical intersection. The three-state Hamiltonian includes all terms through second order in both the diagonal and off-diagonal blocks. Its construction is accomplished in two steps. First, a nascent Hamiltonian, centered at the lowest energy two-state conical intersection, is determined using ab initio gradients and derivative couplings. Then, the nascent Hamiltonian is improved by optimizing selected contributions to the second-order coefficients to better reproduce relevant minima and harmonic frequencies. This Hamiltonian is then expressed in a basis tailored to describe the neutral states of interest under the multimode vibronic coupling approximation. The vibronic Hamiltonian is diagonalized to obtain negative ion photoelectron spectra for pyrazolide-h(3) and the completely deuterated analog pyrazolide-d(3). The resultant spectra, determined employing vibronic Hamiltonians as large as 500 million terms, compare favorably to recent theoretical and spectroscopic results for pyrazolyl-d(3) and to spectroscopic results for pyrazolyl-h(3), for which no reliable simulations had been available.     

High-resolution photoelectron spectrum of ozone

The photoelectron spectra of ozone have been recorded and the first three electronic band systems reassigned on the basis of observed vibrational structure and calculations reported in the literature. The systems X?,Ã, and B? at 12.75, 13.03, and 13.57 eV are assigned as ²A₁, ²A₂, and ²B₂, respectively.     

The photoelectron spectrum of methylisocyanide-borane

The He(1) resonance photoelectron spectrum of the methylisocyanide-borane complex is reported in the range 6–21 eV. This information together with that previously recorded for free methylisocyanide is correlated with ab-initio 4–31G molecular orbital calculations on both species at their experimental geometries. The results are interpreted with respect to changes in the bonding character of the electron donor on complex formation.     

A theoretical study of the second band of the photoelectron spectrum of benzene with an analysis of the vibrational structure

Ab initio calculations have been performed to study the second band of the photoelectron spectrum of benzene with analysis of the vibrational structure. The ²E_{2 g} and ²A_{2 u} states contribute to this band. In this study each contribution to the band is discussed. We propose that the onset of the band should be assigned to the 0-0 transition of the ²A_{2 u} state. Received: 20 August 1998 / Accepted: 15 January 1999 / Published online: 7 June 1999     

Deprotonated cytosine anions: a theoretical prediction of photoelectron spectra

Predictions on the photoelectron spectra of deprotonated cytosine anions (cytosinate, Cye(-)) have been made with ab initio electron propagator methods. Two imino-oxo forms are most stable, but four other isomers have energies within 10 kcal/mol. The first vertical electron detachment energies (VEDEs) for the three most stable Cye(-) isomers are approximately 3.4 eV. Imino-oxy VEDEs are about 0.3 eV smaller. For each anion, the lowest VEDE corresponds to a pi Dyson orbital. The order of higher final states is changed when relaxation and correlation effects are considered. Considerable mixing between lone-pair and bonding lobes occurs in the sigma Dyson orbitals.     

Broad photoelectron spectrum and lowered electron affinity due to hydrogen in ZnOH: a joint experimental and theoretical study

We report a combined experimental and theoretical photoelectron spectroscopy study of ZnOH(-). We find that the electron binding energy spectrum of ZnOH(-) reveals a broad and featureless peak between 1.4 and 2.4 eV in energy. The vertical detachment energy (VDE) of ZnOH(-) is determined to be 1.78 eV, which is lower than the 2.08 eV VDE of ZnO(-). Our theoretical calculations match the VDE of ZnOH(-) accurately, but we find that the broadness of the peak cannot be explained by rotational or vibrational state excitation. The broadness of this peak is in strong contrast to the narrow and easily understood first peak of the ZnO spectrum, which features a well-resolved vibrational progression that can be readily explained by calculating the Franck-Condon transition factors. This study provides spectroscopic evidence of the effect of hydrogen on diatomic ZnO.     

The photoelectron spectrum of ethylene sulphide

The He I photoelectron spectrum of ethylene sulphide is reported. There are six ionization potentials below 21 eV, the first, corresponding to ionization from a predominantly sulphur 3p orbital, occurring at 9.05 eV. The orbital types and symmetries have been assigned on the basis of semi-empirical calculations. The results indicate that in this highly strained cyclic compound sulphur d-orbital participation may be important.     

The photoelectron spectrum of phosphorus pentafluoride

The He(I) photoelectron spectrum of PF₅ has been determined. Assignments for the six observed bands are suggested and comparisons with several semi-empirical molecular orbital calculations are made. Particular interest is associated with the fifth band since it exhibits vibrational fine structure.     

Surface relaxation in water clusters: evidence from theoretical analysis of the oxygen 1s photoelectron spectrum

We present a theoretical interpretation of the oxygen 1s photoelectron spectrum published by Ohrwall et al. [J. Chem. Phys. 123, 054310 (2005)]. A water cluster that contains 200 molecules was simulated at 215 K using the polarizable AMOEBA force field. The force field predicts longer O...O distances at the cluster surface than in the bulk. Comparisons to ab initio molecular dynamics (MD) simulations indicate that the force field underestimates the degree of surface relaxation. By comparing cluster lineshape models, computed from MD simulations, to the experimental spectrum we find further evidence of surface relaxation.     

The threshold photoelectron spectrum of silane

The threshold photoelectron spectrum of SiH₄, has been recorded between 11 and 20 eV. The vibrational structure observed in the first band of the HeI PES could not be detected. Between 15 and 18 eV. autoionizing Rydberg states converging to the ²A₁ ionisation limit are observed. They can be interpreted as excitations to npt₂ or ndt₂ orbitals.     

The microwave spectrum and electronic structure of cyanogen azide

The rotational spectrum of cyanogen azide has been assigned and yields values of A = 38.06737 GHz, B = 3.18517 GHz and C = 2.93357 GHz. The measured dipole moment components of μ_a = 2.96 D, μ_b = 0.44 D. μ_total = 2.99 D are compared with those computed using a CNDO/2 approach for NCN₃ and several related molecules.     

CO activation by the heterobinuclear transition metal-iron clusters:A photoelectron spectroscopic and theoretical study

Spectroscopic characterization of CO activation on multiple metal-containing catalysts remains an impor-tant and challenging goal for identifying the structure ...     

The X-ray photoelectron spectrum of sulphur vapour

The X-ray photoelectron spectrum of S₈ vapour obtained with Al Kα radiation in a spectrometer designed for high temperature work is reported. The S2s and 2p levels were found to lie at 10.1(1) eV and 10.5(1) eV lower binding energy than the corresponding levels in SF₆ and 0.5 eV lower than the levels in H₂S. A S2p/S2s intensity ratio per electron of 0.40(3) was determined, in very good agreement with theory. The photoelectron spectrum in the molecular optical region was obtained and is in good agreement with a previously published spectrum of sulphur powder.