Ab initio calculations on vibronic coupling in the lower triplet states of pyrimidine

Author(s):
Buma, W.J.; Donckers, M.C.J.M.; Groenen, E.J.J. (0000-0001-7530-9211)
Published
1992
Publication type
Article / Letter to editor

Abstract

Ab-initio calculations at the UHF and CASSCF levels have been performed in which the geometry of pyrimidine in the B-3(1)(npi*), 3A2(npi*), and 3A1(pipi*) states has been optimized. The calculations clearly demonstrate the influence of vibronic coupling on the molecular and electronic structure of the molecule in these states. For the npi* states, conformations corresponding to minimum energy are found that deviate significantly from planar. For the 3A1(pipi*) state, vibronic coupling similar to that between the B-3(1u) and 3E1u states of benzene has been found. From the calculations, we deduce a dynamic out-of-plane distortion of the molecule in the B-3(1u)(npi*) state, which provides for a coherent description of the results of optical and magnetic-resonance data available for the lowest triplet state of pyrimidine. The out-of-plane distortions occurring in the B-3(1)(npi*) and 3A2(npi*) states conform to the increased antibonding character of the pi-electron system upon npi* excitation.

Date issued
1992-11-18
Language
English
Publisher
AMER CHEMICAL SOC
Is part of
Journal of the American Chemical Society (1992), Vol. 114, no. 24, p. 9544-9551
hdl
1887/3590354
doi
10.1021/ja00050a038
URL
https://pubs.acs.org/doi/abs/10.1021/ja00050a038