LASER-INDUCED FLUORESCENCE EXCITATION-SPECTRA OF INDOLINE - LOW-FREQUENCY VIBRATIONS OF THE PSEUDO-4-MEMBERED RING

The laser-induced fluorescence excitation (FE) and single vibronic lev el luminescence (SVL) spectra of indoline have been studied by a pulse d seeded jet technique. The vibronic spectrum bears the signature of t wo low-frequency vibrations involving coupling of C-2-puckering and N- inversion. A low-frequency (122 cm(-1)) regular progression in the FE spectrum has been assigned to a coupled vibration involving C-2-pucker ing and N-inversion. The corresponding ground state frequency, as obta ined from SVL spectra, is 160 cm(-1). Another series of bands with irr egular intervals has been fitted with a double-well potential barrier of 33 cm(-1) this corresponds to the second coupled vibration of C-2-p uckering and N-inversion. On substituting the H atom attached to the N atom by a D atom, a large isotope shift is obtained. This is explaine d as being due to a large difference in N-H vibrational frequencies of S-0 and S-1 states.