Radiative decay and radiationless deactivation in selectively excited CN

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Abstract
Individual vibrational levels (v=3–9) of the A 2Π state of the CN radical are excited by a tunable dye laser. The time and wavelength resolved fluorescence of the selectively excited levels is then recorded as a function of the Ar carrier gas pressure. It is found that the decay of many levels is, particularly at lower pressures, strongly double exponential, with the longer component time constant considerably in excess of the CN A 2Π radiative lifetime. The short time constant portion of this exponential is interpreted in terms of a model which includes fast collisional equilibration between the excited v′A 2Π level and a nearby v″, X 2Σ level. The slower part of the decay consists of quenching and radiative decay from the coupled levels. Approximate values for the rate constants governing these processes are derived.