Journal article
The photoelectron spectra of the isomeric 1- and 2-methyltetrazoles; their equilibrium structures and vibrational analysis by ab initio calculations
The Journal of chemical physics, Vol.149(3), pp.034305-034305
07/21/2018
Handle:
https://hdl.handle.net/2376/100518
PMID: 30037262
Abstract
New synchrotron based studies of the photoelectron ionization spectra (PES) for the isomeric 1- and 2-methyltetrazoles (1- and 2-MeTet) show markedly higher resolution than previous reports. The unusual spectral profiles suggest that a considerable overlay of the ionic states occurs for both molecules. Under these circumstances of near degeneracy of two or more ionic states, mutual annihilation of vibrational fine structure occurs for all except the strongest vibrational states; the PES just reflects the resultants rather than full spectra. Theoretical determination of the adiabatic ionization energies (AIEs) proved a challenge; the most successful method was second order Møller-Plesset perturbation theory (MP2). These calculations suggest that the lowest PES bands for both isomers contain ionization both from lone pair σ-orbitals (
A') on the N-atoms (LP
) and π-orbitals (
A″). The lowest experimental AIEs are as follows: 1-MeTet is 10.315 eV assigned to 1
A', while 2-MeTet is 10.543 eV assigned to 1
A″. Franck-Condon analysis shows that the lowest ionization energy regions of both spectra are dominated by IE from the LP
A' manifold, even though the
A″ states have a higher absolute intensity. In this example, we have utilized a VUV Rydberg state to assist simplification of the PES; more frequently, the PES assignment is simpler and assists the location of Rydberg states in the VUV. The very slow spectral onset for 2-MeTet demonstrates the importance of vertical ionization energy calculations since maxima are more readily measured than slow onsets. These were performed at the equilibrium structure of the X
A' state, using both multi-reference multi-root configuration interaction and the ionization potential variant of the equations-of-motion coupled cluster method, with single and double excitations (EOMIP-CCSD). This enabled the principal ionization bands to be identified over a wider range of energy. Attempts to study the higher ionic states by EOMIP-CCSD showed that several states of each symmetry are close to degenerate for 1-MeTet, in particular. A multi-configuration self-consistent field study confirmed the small separation of ionic states, but state switching during the optimization process largely disabled this method.
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Details
- Title
- The photoelectron spectra of the isomeric 1- and 2-methyltetrazoles; their equilibrium structures and vibrational analysis by ab initio calculations
- Creators
- Michael H Palmer - School of Chemistry, University of Edinburgh, Joseph Black Building, David Brewster Road, Edinburgh EH9 3FJ, Scotland, United KingdomMarcello Coreno - ISM-CNR, Istituto di Struttura della Materia, LD2 Unit, 34149 Trieste, ItalyMonica de Simone - IOM-CNR Laboratorio TASC, Trieste, ItalyCesare Grazioli - ISM-CNR, Istituto di Struttura della Materia, LD2 Unit, 34149 Trieste, ItalySøren Vrønning Hoffmann - ISA, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, DenmarkNykola C Jones - ISA, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, DenmarkKirk A Peterson - Washington State University, Department of Chemistry, Pullman, Washington 99164-4630, USAR Alan Aitken - School of Chemistry, University of St Andrews, North Haugh, St Andrews, Fife KY16 9ST, United KingdomCécile Rouxel - School of Chemistry, University of St Andrews, North Haugh, St Andrews, Fife KY16 9ST, United Kingdom
- Publication Details
- The Journal of chemical physics, Vol.149(3), pp.034305-034305
- Academic Unit
- Chemistry, Department of
- Publisher
- United States
- Identifiers
- 99900546511201842
- Language
- English
- Resource Type
- Journal article