Time and frequency resolved dynamics of ArBr2

We report the first spectroscopic observation of and vibrational predissociation dynamics for ArBr2. Measurements are reported for the linear and T-shaped isomers with time and frequency resolution near the Fourier limit of a 15 ps pulse. For the T-shaped isomer, the Ar-Br-2 bond energy D-0 for the B state, nu(')=19, is found to be 200 cm(-1), yielding a D-0(X) value of 213 cm(-1). Product appearance rates are determined for nu(')=16-25 of the B state of ArBr2. While the rate generally increases with increasing vibrational quantum number, the trend is not monotonic. Also, obtaining reproducible rates for any given vibrational level requires very careful control of the experimental conditions. The data suggest that ArBr2 undergoes vibrational predissociation (VP) in the sparse intramolecular vibrational relaxation regime. These observations are consistent with theoretical calculations that show that T-shaped ArBr2 undergoes VP in the sparse regime, such that lifetimes are strongly dependent on both the vibrational and rotational quantum numbers. As for ArI2, a linear isomer of ArBr2 is found to contribute a quasicontinuous background to the excitation spectra. Direct excitation of this continuum results in a very broad product vibrational distribution.