Steady-state and time-resolved luminescence spectroscopy of atomic zinc isolated in thin film samples of the solid rare gases, prepared by the cocondensation of zinc vapor with argon, krypton, and xenon has been recorded at 6.3 K using synchrotron radiation. Pairs of emission bands result from photoexcitation of the singlet 4p 1 P 1 ←4s 1 S 0 resonance transition of atomic zinc, even in annealed samples. In Zn/Ar the pair of emission bands were observed in the uv at 218.9 and 238 nm and for Zn/Xe in the near-uv at 356 and 399 nm. For the Zn/Kr system two emission bands were observed in the uv region at 239.5 and 259 nm but in addition, a weaker band was present in the near-uv at 315.6 nm. In a given annealed rare-gas host, the excitation profiles recorded for all the emission bands are identical, exhibiting the threefold splitting characteristic of Jahn-Teller coupling in the triply degenerate excited 1 P 1 state. These excitation profiles are identified as the solid phase equivalent of the 4p 1 P 1 ←4s 1 S 0 resonance transition of atomic zinc occurring at 213.9 nm in the gas phase. Based on their spectral positions and temporal decay characteristics, the emission bands observed in the uv and near-uv spectral regions have been assigned as the singlet and triplet transitions, respectively, of atomic zinc. The origin of the pairs of emission bands is ascribed to the Jahn-Teller coupling between noncubic vibronic modes of the lattice and the excited 4p orbital of the 1 P 1 state of atomic zinc, resulting in the coexistence of two energy minima. In Zn/Ar, the effects of slow vibrational relaxation in the excited singlet state were evident in the relative intensities and temporal decay profiles of the pair of emission bands. Specifically, the lower energy emission band was favored with excitation of the highest energy component of the threefold split Jahn-Teller absorption band, while the higher-energy emission was favored with excitation of the lowest-energy component. The intensity of the triplet state emission was observed to be enhanced in the heavier rare gases, being completely absent in Ar, weak in Kr, and the only emission observed in Xe.
The temperature dependence of the pairs of emission bands present for atomic zinc isolated in annealed solid argon, krypton, and xenon samples is examined in steady-state and time-resolved luminescence spectroscopy. The pairs of emission bands in all the Zn/RG systems exhibited a reversible temperature dependence whereby the intensity of the high-energy band decreased, while the low-energy band gained in intensity with increasing temperature. In the Zn/Ar system, the decrease in the intensity of the 218.9 nm emission band observed between 9 and 28 K was coupled with a concomitant increase in the intensity of the band at 238 nm. In this temperature range the decay times of the 218.9 nm band decreased while the 238 nm band exhibited a constant decay time of 1.41 ns and a rise time correlated with the decay of the 218.9 nm band. The interdependence exhibited by the intensities and decay times of the two emission bands is modeled by an activated nonradiative process with a barrier height of 130.6 cm Ϫ1 for population interconversion between the pairs of emitting levels on of the spin singlet adiabatic potential energy surface. Similar behavior was observed in Zn/Kr between 6.3 to 20 K, but at higher temperatures this system also exhibited enhanced intersystem crossing. Likewise, for Zn/Xe, the low-energy 399 nm emission increased in intensity at the expense of the high-energy 356 nm emission up to a temperature of 40 K. For the Zn/Kr pair of singlet emissions and the Zn/Xe pair of triplet emissions, barrier heights of 78.1 and 42.6 cm Ϫ1 were evaluated, respectively.
The IR spectroscopy of matrix-isolated DMZ is presented as a precursor for the analysis of DMZ photochemistry in the solid rare gases. In agreement with gas-phase work, the present study reassigns the band observed at 1309.2 cm -1 , currently assigned in the matrix literature to the bending mode of the impurity methane, to the ν 10 + ν 14 band combination mode of DMZ. From a combination of IR absorption and UV luminescence studies, atomic zinc and a pair of methyl radicals (Zn + 2CH 3 ) are identified as the photochemical products formed with ArF excimer laser photolysis. A concerted dissociation pathway of DMZ in solid Ar is considered to be the only mechanism leading to the production of methyl radicals in the vicinity of ground-state atomic zinc. The lack of observation of the methylzinc (CH 3 Zn) and methyl radicals as products is explained in terms of the rapid geminate recombination of these radicals in the matrix cage, which in turn explains the poor efficiency of DMZ dissociation in the solid. Evidence exists for the formation of secondary products with ArF photolysis, namely, the production of ethylzinc hydride and acetylene. It is proposed that the former arises from the excited-state insertion of atomic zinc into the C-H bonds of the small amounts of ethane arising from the recombination of the methyl radicals. Acetylene is a product of ArF dissociation of ethylene which results from recombination of hot methyl radicals.
Absorption spectra of thin-film DMZ/Ar samples, prepared by condensing gaseous mixtures of dimethylzinc (DMZ) with argon at 12 K, were recorded in the region of the first dissociative absorptions of DMZ centered in the gas phase at 200 nm. Large blue shifts are observed in the matrix spectra which can be related to the Rydberg-like characteristics of these excited states of DMZ. The photochemistry of DMZ in an argon matrix was investigated either by subjecting samples to undispersed synchrotron irradiation using a quartz filter to select a wavelength range above 155 nm or to wavelength-specific irradiation. Steady-state and time-resolved luminescence spectroscopy of the dissociation products isolated in solid argon indicate the existence of atomic zinc strongly perturbed by a methyl radical in freshly photolyzed samples, which yields truly isolated atomic zinc upon annealing to 33 K. Dissociation threshold measurements indicate a barrier of 25 kcal/mol for direct cage escape of atomic zinc in the Ar lattice. The increased intensity of Zn( 3 P 1 )/Ar emission observed in photolyzed DMZ/Ar samples relative to pure Zn/Ar samples is explained in terms of the enhanced ISC of atomic zinc in the presence of hydrocarbon species in the former samples. This has been shown by codeposition of atomic zinc with Ar doped with CH 4 and C 2 H 6 .
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