Isotopomer-selective overtone spectroscopy by ionization detected IR+UV double resonance of jet-cooled aniline

We report the analysis of the NH-stretching overtone absorption of gas-phase aniline C(6)H(5)NH(2) and C(6)H(5)NHD between 6500 and 7100 cm(-1). Spectra of jet-cooled aniline are obtained by a new IR + UV double resonance scheme, where vibrationally excited aniline is ionised by resonantly enhanced two-photon ionisation via hot-hands of the S(1) <-- S(0) transition. Ionisation detection in a time-of-flight mass spectrometer allows observing isotopomer-selective overtone spectra (ISOS), for example of C(6)H(5)NHD, which occurs in a mixture with C(6)H(5)NH(2) and C(6)H(5)ND(2). For C(6)H(5)NH(2), a strong Fermi resonance between the symmetric MI-stretching and the symmetric NH-bending vibration is identified, with a coupling matrix element W approximate to 47 cm(-1). Fire also discuss the interplay of stereomutation on the femtosecond timescale and excitation of high-frequency stretching modes. (C) 1998 Elsevier Science B.V. All rights reserved.