Spectroscopy and Photodissociation of Dimethylzinc in Solid Argon. 1. Vacuum UV Luminescence Detection/Synchrotron Radiation Photolysis

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(3P1)/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 co-deposition of atomic zinc with Ar doped with CH4 and C2H6.