No abstract

Vibrational transition probabilities have been measured for the B2Z+(u'=0_3)"2~(~''=Ck10) and B'2A(u'=0, 1)-X211(u"=0_2) systems of SiCl. Individual vibronic levels of the excited states were prepared by laser excitation of ground-state Sic1 formed in a discharge-flow system, and the resultant emission was dispersed and recorded. Independent measurements made in two laboratories were in very satisfactory agreement. The extensive results for the B-X system were compared with Franck-Condon factors derived from Rydberg-Klein-Rees potentials, allowing the form of the electronic transition dipole moment function to be assessed. It was found that the electronic transition probability for the B-X system is relatively slowly varying with internuclear distance, consistent with previous conclusions on the electronic configurations of the states involved. The more limited data on the strongly diagonal Bf-X system were not readily reproduced from the accepted form of the potentials and the anticipated electronic transition dipole moment.

The collisional quenching of selected vibrational levels of electronically excited Sic1 B'ZA radicals by the series of nonpolar molecules He, Ar, H2, N2, C02, CH4, and CF4 was investigated experimentally. The results for He and Ar agreed well with previous independent measurements. Rate constants (and cross sections) for total removal of Sic1 B12A v' = 0 and 1 are relatively large for all collision partners and quite well correlated with the attractive nature of the intermolecular interaction. Rate constants and cross sections were measured for transfer to the near-degenerate B2Z+ electronic state. A substantial, but variable, fraction of the total removal proceeds via this channel for all quenchers. Nascent vibrational distributions over the V I = 0, 1, and 2 vibrational levels of the B2Z+ state were determined by exploiting the relatively much shorter radiative lifetime of this electronic state. N o obvious, single molecular property could be identified to explain these vibrational distributions.There is, however, a trend toward removal of more energy by polyatomic molecules. The cross sections for the single, near-resonant state-to-state process B12A v' = 0 to BZZ+ u' = 2 were found to be well-correlated with attractive intermolecular forces. Selected higher resolution measurements confirmed the lack of any significant vibrational relaxation within the B'2A state competitive with collisional transfer to the B2Z+ state and revealed no evidence for preferred interstate transfer through specific -gatewayn rotational levels.