Vibrational transition probabilities in the B-X and B'-X systems of the chlorosilylidyne radical

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.

State-to-state collisional energy transfer in electronically excited silicon monochloride radicals

“…In Figure 6a(i), the laser was tuned to the Qi head of the B-X1/2 (1-0) band, and therefore overlapped predominantly transitions from low rotational states. 31 The fluorescence was resolved on the B-X3/2 (1,0) transition to the other spin-orbit component of the ground state, thereby avoiding scattered laser light. In contrast, in Figure 6b(i), the excitation laser was tuned 32 cm"1 to higher wavenumber, which would then predominantly excite transitions from substantially higher rotational states.…”

“…The B'-X3/2 (0,0) rotational envelope is, perhaps not surprisingly, characteristic of a near-thermal rotational distribution. 31 The similarity of rotational constants in the B' and X states means that a wide range of rotational levels would be excited within the finite bandwidth of the excitation laser when it is centered on the Qi head. Rotational relaxation within the B' state is also expected to be competitive with the interstate transfer to the B state, and to be faster than the rate of B'-X emission at the typical pressures of these experiments.…”

“…31 This relatively simple experimental procedure successfully yields nascent vibrational populations in the B22+ state because of the fortuitously dissimilar radiative lifetimes of these electronic states. Collisions transfer a certain proportion of the molecules to the lower-lying u' = 0, 1, and 2 vibrational levels of the B2Z+ state.…”

“…In a previous joint publication, 31 we have presented the spectroscopic information on SiCl necessary for this and Jeffries '30 energy-transfer studies. The region of the intersecting '2and B22+-state potential energy curves of most interest in these investigations is shown in Figure 1.…”

“…The curves were constructed by the RKR procedure,32"34 using published molecular constants as described in our earlier work. 31 Energy gaps (in cm'1 units) between the relevant rotationless vibronic levels are included in the figure. This relatively simple experimental procedure successfully yields nascent vibrational populations in the B22+ state because of the fortuitously dissimilar radiative lifetimes of these electronic states.…”