Relaxation of the first excited 1u state of Hg2

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Abstract
The decay of the 335 nm Hg2 fluorescence band was measured with 1 nsec time resolution for the first 200 nsec following optical excitation by a 10 nsec laser pulse. Measurements of the decay rates for various wavelengths in this band were used to analyze the relaxation of the vibrational levels in the 1u state. It was found that the lower vibrational levels quickly reach a Boltzmann distribution described by an effective temperature Teff. This effective temperature then decreases with time, asymptotically approaching the gas temperature. Comparison of these data with a model calculation by Montroll and Shuler yields a transition rate of 5.2×10−11 cm3 sec−1 for the transition between the two lowest vibrational states. Analysis of the relaxation for higher vibrational levels gave a value of 2.7×10−10 cm3 sec−1 for the 1u→0−g transition rate. Since no mercury trimers have been formed at these early times, the 485 nm fluorescence band is not present. It was therefore possible to evaluate the repulsive wall of the 1u potential curve for small internuclear distances corresponding to wavelengths in the red wing of the 335 nm dimer band which are normally overlapped by the 485 nm trimer band.