Time Resolved Visible and UV Absorption Spectroscopy of Bromine Clusters in Argon Matrices

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Abstract
Matrix deposition was observed by a laser interference technique at deposition rates of 0.1 – 0.2 mmol/h at T = 10 K up to a matrix thickness of 1.1 · 10−4 m. Absorption spectra of Br2/Ar matrices (1 : 1000 – 1 : 300) examined quantitatively at λ = 300 nm and 415 nm showed an increase of molar bromine absorptivity with increasing Br2‐concentration. The increase of absorptivity may be explained by formation of Br2‐dimers during matrix deposition. Br2/Ar matrices were exposed to laser pulses at λ = 490 nm and showed a transient increase of absorption in the near UV (λ < 370 nm), a spectral region mainly due to Br2‐dimers. This increase presumably depends on laser excitation of Br2‐molecules situated in dimers into the B3π(O) state followed by deactivation into the ground state X1Σ. At least three exponentials are necessary to fit the transient signals with the lifetimes t1 = 3.5 μsec, t2 = 64 μsec, t3 = in the order of some msec.

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