Highly resolved UV spectroscopy: Structure of S-1 benzonitrile and benzonitrile-argon by correlation automated rotational fitting

Highly resolved UV spectra of benzonitrile and benzonitrile-argon were measured by resonance enhanced two-photon ionization. Rotational constants are obtained by correlation automated rotational fitting (CARF) of the rotational fine structure in the spectra. For the benzonitrile monomer the observed line width of less than 100 MHz points to a relaxation rate smaller than 10(9) s(-1). The main origin for the nonradiative relaxation is expected to be internal conversion to the S-1 charge transfer state. The position of the Ar atom in electronically excited (S-1) benzonitrile-argon is 3.48(1) Angstrom above the molecular plane with a slight displacement of 0.535(4) Angstrom towards the C-N group. (C) 1997 Elsevier Science B.V.