A. Nino et al., WAGGING AND TORSION VIBRONIC STRUCTURE IN THE T-1 [- S-0 ELECTRONIC-SPECTRUM OF ACETALDEHYDE, Journal of physical chemistry, 98(6), 1994, pp. 1519-1524
The T-1 <-- S-0 electronic band spectrum in acetaldehyde was simulated
from RHF and UHF/MP2/6-311G(d,p) ab initio calculations for the two e
lectronic states. The torsion-wagging energy levels were evaluated by
the variational method using free rotor basis functions expressed as s
ymmetrized double-Fourier expansions. A comparison of the calculated b
and spectrum to the long-path absorption spectrum allowed for the assi
gnment of a number of clearly defined bands and placed the origin at 2
7 240 cm(-1). The calculated height of the barrier to internal rotatio
n for the lower S-0 state of 415 cm(-1) yielded levels in excellent ag
reement with the torsional levels derived from far infrared measuremen
ts. The calculated T-1 excited-state barrier heights for the pure tors
ion and wagging motions were 647 and 968 cm(-1). The corresponding val
ues in the S-1 state are 709 and 776 cm(-1).