Vector and scalar correlations in the photodissociation of NCCN

✍ Scribed by Ming Wu; Gregory E. Hall

• Publisher: Elsevier Science
• Year: 1994
• Tongue: English
• Weight: 759 KB
• Volume: 80
• Category: Article
• ISSN: 1010-6030
• DOI: 10.1016/1010-6030(94)01053-6

✦ Synopsis

The CN photofragments from the photodissociation of NCCN at 193 nm have been measured by high-resolution transient absorption spectroscopy. Doppler-broadened profiles of isolated rotational lines in the 2-O and 3-l vibrational bands of the CN A-X transition were observed under collisionless conditions with a tunable, singlefrequency Ti:sapphire ring laser. Analysis of the Doppler profiles reveals a vector correlation between the translation and rotation of CN photoproducts, with the angular momentum of the high rotational states increasingly perpendicular to the recoil velocity. After correction for vector correlations, the laboratory-frame scalar speed distribution of state-selected photoproducts can be determined. The mean squared laboratory velocity is directly related to the average internal energy of coincident CN fragments. The wings of the Doppler profiles indicate that the available energy for a pair of ground state CN photoproducts following 193 nm dissociation of NCCN at 295 K is 5300& 150 cm-', which includes the average vibrational energy of the parent molecules selected by tbe photolysis laser. Phase space theory with an optimized available energy of 5300 cm-' produces laboratory speed distributions that are in qualitatively reasonable agreement with the kinetic energy measurements, but overestimate the total internal energy of the photofragments. The measurements are good enough to warrant comparison with more sophisticated models of unimolecular decomposition.