Excited-State Structural Dynamics of Propanil in the S sub(2) State: Resonance Raman and First-Principle Investigation

Resonance Raman (RR) spectra and quantum chemical calculations were used to investigate the photodissociation dynamics of propanil in the S sub(2) state. The RR spectra indicate that the photorelaxation dynamics for the S sub(0) arrow right S sub(2) excited state of propanil is predominantly along nine motions: C=O stretch, nu sub(51) (1659 cm super(-1)), ring C=C stretch, nu sub(50) (1590 cm super(-1)), NH wag/ring C=C stretch, nu sub(49) (1534 cm super(-1)), ring CCH in-plane bend/NH wag, nu sub(42) (1383 cm super(-1)), NH wag/-CH sub(2)- rock, nu sub(41) (1353 cm super(-1)), ring C=C stretch/NH wag/-CH sub(2)- rock in-plane, nu sub(40) (1299 cm super(-1)), Ph-NH stretch/ring CCH in-plane bend, nu sub(37) (1236 cm super(-1)), ring CCH in-plane bend, nu sub(35) (1150 cm super(-1)), -CH sub(2)CH sub(3) twist, nu sub(33) (1080 cm super(-1)), ring trigonal bend, nu sub(31) (1029 cm super(-1)), ring CCH bend out-of-plane, nu sub(27) (899 cm super(-1)), whole skeleton deformation in-plane, nu sub(20)(688 cm super(-1)). Strong electron coupling between S sub(1) and S sub(2) of propanil is found by quantum chemistry calculations and depolarization spectra. The excited-state dynamics of the S sub(2) state is discussed, and the results are compared with the previously reported results for formanilide to examine the Cl substitution effect.