Photophysical properties of matrix-isolated Mg2: Evidence for efficient predissociation

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Abstract
Optical absorption and excitation profiles recorded for emission of magnesium dimer in argon and krypton matrices allow identification of the A 1Σ+u and B 1Πu states. The radiative lifetime measured for the lowest vibrational levels of the A 1Σ+u state is 1.0 ± 0.25 ns in Ar consistent with a strongly allowed A 1Σ+u–X 1Σ+g transition. Excitation into the higher vibrational levels produces a rise time of 0.5 ± 0.25 ns in the A→X emission, indicating the rate of vibrational relaxation under solid state conditions. Photoexcitation into the higher vibrational levels of the A 1Σ+u state also produces atomic triplet emission by a mechanism of homogeneous predissociation occuring via coupling of this bound, optically active state with the repulsive, optically inactive 3Πu state. The enhancement of predissociation in solid krypton compared with argon is interpreted in terms of the greater overlap of the coupling states in the former solid which is facilitated by the differential shifting of the bound and repulsive dimer states in the two solids. From the observations that the bound A 1Σ+u state is stabilized while predissociation occurs for lower vibrational levels in Kr relative to Ar, it is concluded that the repulsive 3Πu state crosses the bound state on its inner limb.