Comparative studies of the photoinduced reactions in the Mg[sup +]–SCNC[sub 2]H[sub 5] and Mg[sup +]–NCSC[sub 2]H[sub 5] complexes.

The photoinduced reactions of the complexes Mg[sup +]–SCNC[sub 2]H[sub 5] and Mg[sup +]–NCSC[sub 2]H[sub 5] are studied comparatively in the spectral range of 230–440 nm. One-photon excitation of the complexes through the Mg[sup +] chromophore (3 [sup 2]P←3 [sup 2]S) gives rise to the evaporative fragment as well as the molecular activation and charge transfer products. The action spectra of the complexes consist of three broad peaks for Mg[sup +]–SCNC[sub 2]H[sub 5] and two for Mg[sup +]–NCSC[sub 2]H[sub 5], which accord with the structures obtained from quantum mechanics calculations. These calculations reveal two association isomers for Mg[sup +]–SCNC[sub 2]H[sub 5]: one is with Mg[sup +] being linked to the S atom and the other to the N atom. The former is more stable than the latter by only 0.23 eV. Both of the isomers have been shown to exist in the complex source employed in our experiments. On the other hand, only one stable structure is found for the complex Mg[sup +]–NCSC[sub 2]H[sub 5] characterized by the Mg[sup +]–N linkage. In general, the photofragments are dominated by Mg[sup +] at λ>400 nm, which decreases with decreasing wavelength accompanied by the increase in other photoproducts. In addition, the branching ratios of Mg[sup +] to other photoproducts are nearly constant in the short wavelength region but decrease with decreasing wavelength. The observed photoreactions have been reasonably explained. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]