Internal rotation in high-resolution ultraviolet spectra.: II.: Spectrum and structure of the aniline-nitrogen van der Waals complex

Rotationally resolved S-1<--S-0 electronic spectra of the nitrogen complex of aniline have been observed. The spectra are split into two subbands due to internal rotation of N-2. The analysis of the rotational constants reveals that N-2 is located above the ring plane of aniline and in the symmetry plane of aniline in the equilibrium position. Barriers hindering internal rotation have been obtained from fitting experimental transitions frequencies using a semirigid C-2v top-C-s frame internal rotation model. Upon excitation into S-1, the distance of N-2 to the ring decreases and the internal rotation barrier increases by a factor larger than 2. Possible reasons for this behavior are discussed. (C) 2001 American Institute of Physics.