Quantitative laser-induced fluorescence spectroscopy of the CF A(2)Sigma(+)-X(2)Pi transition: Electronic transition dipole moment function and predissociation

Several previously unmeasured aspects of the quantitative spectroscopy of the CF A(2) Sigma(+)-X(2) Pi transition have been investigated experimentally. Ground state CF radicals were prepared in an rf discharge chamber and laser-induced fluorescence (LIF) was excited on the A-X transition. Relative vibrational transition probabilities were deduced from dispersed fluorescence spectra emitted by CF A(2) Sigma(+) (upsilon' = 0 and 1), from which the form of the electronic transition dipole moment function, R(e)(r), could be assessed. Reasonable agreement was found with a previous ab initio prediction of a moderate decline in R(e)(r) over the relevant, fairly limited range of internuclear distances sampled by the experiment. Weak fluorescence has also been detected for the first time from the heavily predissociated upsilon' = 2 level. A rotationally-resolved LIF excitation spectrum was obtained. Lower and upper limits on the upsilon' = 2 fluorescence lifetime were estimated to be 0.4 and 2 ns, respectively. There is a weak, if any, decline in the upsilon' = 2 fluorescence quantum yield with rotational quantum number up to ca. 20.5. These observations are shown to be consistent with a predissociation mechanism involving tunneling through the predicted barrier to dissociation which results from an avoided crossing at longer internuclear distances.