Overtonehyphen;excited HN3(Xtilde;thinsp;1Arsquo;): Anharmonic resonance, homogeneous linewidths, and dissociation rates

摘要

Highhyphen;resolution spectra have been obtained for the predissociative Nndash;H stretching overtone levels 5ngr;1(15thinsp;120 cmminus;1) and 6ngr;1(17thinsp;670 cmminus;1) of HN3, cooled in a freehyphen;jet expansion. The spectral bandwidth (Doppler limited at 0.007 cmminus;1full width at halfhyphen;maximum (FWHM) is sufficiently narrow to reveal the homogeneous linewidths of individual rovibrational transitions in the 6ngr;1band, for which we previously measured the dissociation lifetime in timehyphen;domain experiments. Two distinct manifestations of vibrational coupling characterize the spectra: (a) anharmonic mixing of the Nndash;H stretch with other vibrational motions to give a complex spectrum of vibrational eigenstates and (b) homogeneous widths of the resultant states determined by the dissociation lifetime. The results are discussed with reference to previous studies of overtone spectroscopy and intramolecular mixing. Timehyphen;domain measurements of dissociation rates are reported for four vibrational levels with zerohyphen;order labels 5ngr;1+ngr;x. Over the range 15thinsp;100 cmminus;1ndash;17thinsp;700 cmminus;1, the dissociation rate increases monotonically with vibrational energy, with no apparent lsquo;lsquo;modehyphen;specificrsquo;rsquo; variations. This is interpreted in terms of the highly mixed character of any particular vibrational eigenstate that is excited.