A new electronic state of aniline observed in the transient IR absorption spectrum from S1 in a supersonic jet

Newly developed ultraviolet(UV)-infrared(IR) double resonance spectroscopy with relaxed fluorescence, detection has been applied to the observation of the IR spectrum of aniline in the first electronically excited (S-1) state. In the 2900-3900 cm(-1) region above the origin of the S-1 state, two types of IR transitions have been observed. One is the vibrational transition involving the NH2 and CH stretching vibrations in the S-1, state. By examining the IR spectra for several deuterium substituted species, we found that the NH2 stretching vibrations of the S, state are located at 3000 cm(-1), representing extremely large frequency decrease (500 cm(-1)) upon electronic excitation., The other type is the anomalously broad transition appearing above 3300 cm(-1). This transition cannot be assigned to any particular vibrational transition of the S-1 state since it occurs in all the isotopomers examined, and we conclude that it is a vibronic transition to a new electronic excited state, which may be called the new S-2 state. We examined the same energy region by measuring them one-photon laser-induced fluorescence (LIF) and two-photon absorption spectra from the ground electronic (SO) state, and we found an intense band origin of the new S-2 state at 37104 cm(-1) in the two-photon spectrum. From the consideration of the symmetry, the new S-2 state is thought to have B-1 symmetric, species, which is in good agreement with the recent SAC-CI calculation reported by the Nakatsuji group, and the new S-2 state is assigned to the 3s-Rydberg(B-1(1)) state.