Knowledge Bank

Pulsed laser excitation and resolved fluorescence techniques were used to study the $B-X$ and $A-X$ transitions of CN trapped in a solid Ar matrix. Excitation of the $B-X$ system resulted in emissions from the B and A states. The $B-X$ 0-0 transition was blue-shifted by about $200cm-1$ compared to the gas phase position. Due to non-radiative relaxation, the B state lifetime was too fast ($<$20 ns) to be measured using 10 ns excitation pulses. Rapid $B-A$ relaxation resulted in emission from the $A-X$ system. Within the A state, vibrational relaxation competed effectively with radiative decay, preventing the observation of flourescence from levels with $\nu >$3. Wavelength resolved fluorescence spectra showed the 3-0, 2-0, 3-1, 1-0, 0-0, 0-1, 1-2 bands. Analysis of the band positions indicated that the A and X state vibrational constants were unchanged, and the A state electronic term energy blue-shifted by about $200cm-1$, with respect to the gas phase. The sequential cascade of population through the A, $v=3,2,1,$ and 0 levels was evident in the fluorescence decay curves. Analysis of the temporal profiles is in progress.