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ABSTRACT: Vibrational branching ratios have been measured for the H2CO+ X 2B2 state using photoelectron spectroscopy and monochromated synchrotron radiation. In the wavelength range encompassed by the present study the photoionization cross section is dominated by intense autoionizing resonances, most of which belong to Rydberg series converging onto the B 2A1 threshold. Autoionization from these Rydberg states causes considerable variations to be observed in the vibrational branching ratios. The present data have been recorded over several Rydberg members, and the results indicate that autoionization tends to produce a vibrational distribution in the ion that is characteristic of the vibrational level in the neutral excited states.
Journal of Physics B Atomic Molecular and Optical Physics 12/1998; 27(6):1125. · 1.88 Impact Factor
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ABSTRACT: Photoionization of the CO molecule and inner-valence states of CO+ between 22 and 45 eV have been studied by means of photoelectron spectroscopy using both synchrotron radiation and He II radiation. Vibrational structure has been resolved in many bands up to 45 eV. CASSCF (complete active space self-consistent field) and MRCI (multireference configuration interaction) calculations of potential curves in the 22-30 eV range have been performed and these have been used to predict vibrational levels and Franck-Condon factors. In this energy range three valence states, D 2II, 32 Sigma + and 32II have been identified, and spectroscopic constants have been determined for the first two of these. Above 30 eV, all valence states have been found to be repulsive. In addition to the broad bands expected for these states, several progressions of narrow lines are observed most probably reflecting transitions to Rydberg states.
Journal of Physics B Atomic Molecular and Optical Physics 12/1998; 27(20):4915. · 1.88 Impact Factor
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ABSTRACT: The complete valence shell photoelectron spectrum of carbon disulphide has been studied using HeI, HeII and synchrotron radiation. In addition to the photoelectron bands associated with the single-hole ionic states, several satellite features have been observed which are due to multielectron processes. The high resolution HeI and HeII excited spectra have allowed a detailed analysis to be made of the vibrational structure exhibited in the photoelectron bands corresponding to the single-hole and satellite states. The photoelectron spectra recorded with synchrotron radiation demonstrate that the inner valence region contains much complicated structure, and that distinct features are discernible up to a binding energy of at least 34 eV. Many-body Green's function calculations have been performed to evaluate the ionization energies and pole strengths associated with the main lines and satellite lines distributed throughout the valence shell region, and an interpretation of some of the experimental features is proposed, based upon these predictions.
Chemical Physics.
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ABSTRACT: The complete valence shell photoelectron spectrum of the NO2 molecule has been studied in the binding energy range between 10 and 50 eV. HeI and HeII resonance radiation as well as monochromated synchrotron radiation have been used for the ionisation. Assignments have been made for most of the photoelectron bands by comparison with previous theoretical predictions. Photoelectron angular distributions and branching ratios for the bands associated with the outer valence shell have been determined for photon energies between 18 and 120 eV. The HeI and HeII excited spectra have allowed detailed studies to be made of the vibrational fine structure. For the ground ionic state, close lying vibrational lines associated with combined excitations of the symmetric ν1 and the bending ν2 modes have been observed for the first time. Excitation of the asymmetric stretch ν3 mode, in one quantum, is found in the photoelectron band, and its presence is explained in terms of vibronic coupling.
Chemical Physics.
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ABSTRACT: The photoelectron spectrum of benzene has been studied using HeI and synchrotron radiation for the ionisation. The study involves all main bands associated with the single-hole valence states, as well as satellite structure observed in both the outer and the inner valence regions, due to many-electron effects. Many-body Green's function calculations have been carried out employing the ADC(3) approach, and theoretical predictions for the ionisation energies and pole strengths (relative intensities) have been obtained, thus facilitating the interpretation of the experimental results. Photoelectron angular distributions and branching ratios have been determined using monochromated synchrotron radiation in the photon energy range 12–120 eV. HeI excitation has been used to obtain highly resolved spectra and vibrational structure has been studied in the X2E1g, A2E2g, C2E1u, E2B1u and F2A1g ionic states. In the first two bands excitations of Jahn-Teller active modes are found to be important and very good agreement is found with recent theoretical studies of the vibronic structure.
Chemical Physics.
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ABSTRACT: Photoelectron spectra are reported for the inner and outer valence regions of N#2#O for several photon energies up to 120 eV. The outer valence region is characterized by four well resolved bands which can be assigned to ionisation from specific molecular orbitals. In contrast, the inner valence region displays a complex structure, composed of many overlapping lines, extending to a binding energy of approximately 45 eV. The experimental data are compared with theoretical calculations and with a spectrum recorded using X-ray excitation. Several of the features observed in the inner valence region can be interpreted with the aid of theoretical predictions.
Chemical Physics.
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ABSTRACT: The absolute photoabsorption, photoionisation and photodissociation cross sections and the photoionisation quantum efficiency of ethylene and deuterated ethylene have been measured from the ionisation threshold to 500 Å using a double ion chamber and monochromated synchrotron radiation. High resolution photoelectron spectra of the same molecules have been recorded using HeI and HeII radiation, and detailed analyses have been made of the vibrational structure exhibited in the X2B3u, A2B3g, B2Ag, C2B2u and D2B1u photoelectron bands. In the inner valence binding energy region the HeII excited spectrum shows several satellite features which are due to configuration interaction effects. The photoabsorption spectra display extensive vibrational structure extending from the ionisation threshold to approximately 630 Å. With the aid of the high resolution photoelectron spectra, many of these absorption features have been arranged into vibrational progressions associated with Rydberg states. Tentative assignments for some of these states have been proposed based upon an assessment of terms values and quantum defects. A sum rule analysis has been carried out by combining the present absolute photoabsorption measurements with similar data covering the remaining wavelength regions.
Chemical Physics.
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ABSTRACT: The absolute photoabsorption cross section and the photoionization quantum efficiency of nitrous oxide have been measured using a double ion chamber and monochromated synchrotron radiation. In the wavelength range encompassed by the present study the cross section is dominated by intense structure associated with Rydberg series converging onto their the A 2∑+ or the C2∑+ ionization thresholds. Neutral predissociation from these excited molecular states causes significant variations to be observed in the photoionization quantum efficiency. The results indicate that decay from a particular Rydberg member tends to produce an effect on the photoionization quantum efficiency that is characteristic of the series to which that member belongs. The data are discussed in relation to recent theoretical work studying the competition between neutral predissociation and autoionization.
Chemical Physics.
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ABSTRACT: The photoelectron spectrum of the chlorobenzene molecule has been studied using both monochromated synchrotron radiation with photon energies between 15 and 120 eV and HeI radiation at 21.22 eV. Photoelectron angular distributions and branching ratios have been determined over the entire energy range studied. Theoretical investigations have been performed using ab initio SCF and many-body Green’s function methods to evaluate wave functions, binding energies and relative intensities. The ADC(3) calculations of binding energies and pole strengths were particularly important for the interpretation of the inner valence spectrum where electron correlation effects are found to be important. The main part of the photoelectron spectrum is similar to that of benzene but some of the bands are characteristic of the chlorine atom. The Cooper minimum of the Cl 3p orbital is clearly reflected in some of the bands and is used to assess the mixing between ring orbitals and chlorine atomic orbitals. The HeI-excited spectra show extensive vibrational structure in the X̃ 2B1, Ã 2A2, B̃ 2B2, C̃ 2B1 and K̃ 2A1 photoelectron bands. The vibrational structure is analysed in detail and compared to results obtained from multiphoton ionisation photoelectron spectroscopy.
Chemical Physics. 254:385-405.
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ABSTRACT: Vibrational branching ratios have been measured for the CO2+ X 2Πg state using photoelectron spectroscopy and monochromated synchrotron radiation. In the wavelength range encompassed by the present study the photoionization cross section is dominated by intense autoionizing resonances, most of which belong to extended Rydberg series which converse onto either the A 2Πu or the B 2Σu+ thresholds. Autoionization from these Rydberg states causes considerable variations to be observed in the vibrational branching ratios. The present data have been recorded over several members of each Rydberg series, and the results indicate that autoionization from a particular member tends to produce a vibrational distribution characteristic of the series to which that member belongs.
Chemical Physics.
