K. Hottmann

Vibronic coupling effects observed in the high-resolution He(I) photoelectron spectra of BF3

Abstract The He(I) photoelectron spectrum of BF 3 has been measured with an electron energy resolution better than 15 meV. The 1A 2 ′ PE band (IP vert =15.92 eV) reveals vibrational fine structure with intervals of 0.025 eV. In the case of the 2E′ PE band (IP vert =20.08 eV) an additional third progression with intervals of 0.092 eV is observed. The results are discussed on the basis of vibronic interaction between electronic states using symmetry arguments.

Photoelectron spectroscopy of vinylbromide and intramolecular dynamics of the ionic B̃ state

Abstract In this paper, we report the He(I) photoelectron spectrum (PES) and the threshold-photoelectron (TPES) spectrum of C2H3Br. The fine structure observed in the first two ionic states in the He(I) spectrum is assigned to progressions belonging partially to previously unobserved vibrational normal modes. The TPES has been measured between 9.0 and 25.0 eV, and the photon energy range of 9.8–12.0 eV has been investigated in more detail. Extensive calculations with the gaussian set of programs have been performed to help in the assignment of the observed features. Furthermore, a conical intersection between the A 2 A ′′ and the B 2 A ″ states was found to take place along the C–Br stretching coordinate. Intramolecular dynamics of the B 2 A ′′ state, initially prepared in the Frank–Condon region, was probed by the Fourier transform of the spectrum. The B 2 A ′′ state is almost readily depleted, most probably due to a very effective internal conversion through the conical intersection.

He I photoelectron spectroscopy of four isotopologues of formic acid: HCOOH, HCOOD, DCOOH and DCOOD

Abstract He I photoelectron spectra of four isotopologues of formic acid, HCOOH, HCOOD, DCOOH and DCOOD have been measured, mainly with an electron kinetic energy resolution of 15 meV. Quantum chemical calculations of geometries, vibrational mode frequencies and the potential energy distributions characterising each normal mode were made for the neutral 1 1 A ′ ground state, the cation ground state 1 2 A ′ and first excited ion state 1 2 A ″ of the four isotopologues. The results were used to analyse observed vibronic structure in the two PES bands in the 11.3–13.5 eV energy region and this analysis provided values for several vibrational mode frequencies of the ion states. The calculated structure and internal dynamics of the 1 2 A ′ ground state of the ion provide satisfactory agreement with experiment but for the 1 2 A ″ excited state a more refined theoretical treatment, permitting greater structural flexibility, is required. The PES first ionization energy of HCOOH agrees well with that obtained from Rydberg series in absorption spectra, and values more precise than hitherto were obtained for the first and second ionization energies of the four isotopologues. Analysis is also made of PES features concerning the higher energy states of the ions between 12.2 and 21 eV. The adabatic ionization energies of the 2 2 A ′ , 2 2 A ″ , 3 2 A ′ and 4 2 A ′ states in this energy region were determined. Vibrational frequencies were obtained for the 3 2 A ′ ion state of the isotopologues and new assignments were made concerning the energy and structure of the 4 2 A ′ ion state, whose adiabatic energy was found to lie about 60 meV below the 3 2 A ′ state.

The photoabsorption of BF3 in the energy range 6.5-20 eV

Abstract The absorption spectrum of BF 3 has been measured in the photon energy range 6.5–20 eV using monochromatized synchrotron radiation. Assignments have been made on the basis of term value and symmetry arguments. The π→π* (1e″→2a″ 2 ) transition is centered at 13.13 eV, whereas a second excitation to π* (2a′→2a″ 2 ) is located at 17.52 eV. Another valence-type transition (1a′ 2 →5a′ 2 ) is connected with an excitation energy of 15.64 eV. All final states of the valence-type transitions have term values between 3.5 and 4.0 eV. The first member of an n -type Rydberg series converging to the 2E′ ionization energy is assigned to a transition to the Rydberg mixed-valence final orbital 3s+σ* (5a′ 1 ). Members of n p and n d type Rydberg series converging to the 1A′ 2 ionization energy are located in the energy range 13.7⩽ hv ⩽ 15.4 eV. The dense vibrational features centered around 18.5 eV consist of five Rydberg series excited from 2E′. Shape resonance effects in the valence shell spectrum of BF 3 are discussed.

He I photoelectron spectroscopy of formic acid isotopomers HCOOH and DCOOD

Abstract He I photoelectron spectra (PES) of HCOOH and DCOOD have been measured with an electron kinetic energy resolution of 15 meV. Analysis of observed vibronic structure in the two PES bands in the 11.3–13.5 eV energy region provided values for several vibrational modes of the X 2 A ′ and A 2 A ″ electronic states of HCOOH+ and DCOOD+. This analysis is based on the implications of structural changes expected to occur on ionization, using literature values for calculated geometries of these states. The vibronic assignments of both PES bands were consistent with isotopic effects on vibrational mode frequencies and were helped by considerations on relations between carbon–oxygen bond lengths and stretch mode frequencies. The analysis of the second PES band indicates that the calculated structure of the A 2 A ″ state of the ion requires more refined theoretical treatment. The PES first ionization energy of HCOOH agrees well with that obtained from Rydberg series in absorption spectra, and values more precise than hitherto were obtained for the first and second ionization energies of DCOOD, 11.335±0.002 eV and 12.380±0.002 eV respectively, and the second ionization energy of HCOOH, 12.378±0.002 eV.

Photoionization mass spectrometry of kinetic energy-selected ions. An ion retarding potential difference method applied to NO + and O + from N2O

Abstract A new method is described to obtain photoionization efficiency curves of kinetic energy-selected fragment ions. The method is tested and discussed in the case of the dissociative photoionization yields of NO + and O + from N 2 O. The attention is focussed on the dissociative autoionization processes in the threshold region, in the Franck-Condon region of the N 2 O (A 2 Σ + ) state and in the Franck-Condon gap between the A 2 Σ + and B 2 π states.