Microwave and UV excitation spectra of 4-fluorobenzyl alcohol at high resolution. S0 and S1 structures and tunneling motions along the low frequency -CH2OH torsional coordinate in both electronic states

Ryan G Bird; Alexei E Nikolaev; David W Pratt

doi:10.1021/jp2051905

Microwave and UV excitation spectra of 4-fluorobenzyl alcohol at high resolution. S0 and S1 structures and tunneling motions along the low frequency -CH2OH torsional coordinate in both electronic states

J Phys Chem A. 2011 Oct 20;115(41):11369-77. doi: 10.1021/jp2051905. Epub 2011 Jul 27.

Authors

Ryan G Bird¹, Alexei E Nikolaev, David W Pratt

Affiliation

¹ Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States.

PMID: 21790205
DOI: 10.1021/jp2051905

Abstract

Rotationally resolved electronic spectra of several low frequency vibrational bands that appear in the S(1) ← S(0) transition of 4-fluorobenzyl alcohol (4FBA) in the collision-free environment of a molecular beam have been observed and assigned. Each transition is split into two or more components by the tunneling motion of the attached -CH(2)OH group. A similar splitting is observed in the microwave spectrum of 4FBA. Analyses of these data show that 4FBA has a gauche structure in both electronic states, but that the ground state C(1)C(2)-C(7)O dihedral angle of ∼60° changes by ∼30° when the photon is absorbed. The barriers to the torsional motion of the attached -CH(2)OH group are also quite different in the two electronic states; V(2) ∼ 300 cm(-1) high and ∼60° wide in the S(0) state, and V(2) ∼ 300 cm(-1) high and ∼120° wide (or V(2) ∼ 1200 cm(-1) high and ∼60° wide) in the S(1) state. Possible reasons for these behaviors are discussed.

Publication types

Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

Benzyl Compounds / chemistry*
Electrons
Methanol / chemistry*
Microwaves*
Molecular Structure
Quantum Theory*
Spectrophotometry, Ultraviolet

Substances

Benzyl Compounds
Methanol