Photochemical synthesis of new carbon -sulfur and carbon -selenium nanofilms

Broad band solar and Hg-Xe arc source irradiation (300–400 nm) of liquid phase carbon disulfide and gas or liquid phase carbon diselenide produces polymeric films whose average thickness is ∼200 nm. The CS 2 product has an approximate stoichiometry of (CSn) x (n = 1.04–1.05) and is referred to as (CS)x. Using model compounds and 13C labeling in FT-IR studies, a structure is proposed which contains the bond moieties S-S, C-S, C=S, C-C as well as C=C double bonds whose associated absorption frequency is 1431 cm−1 . Strong EPR resonances (g > 2.006) indicative of sulfur-centered radicals from incomplete crosslinking were found in (CS)x, as well as (CS2)x an aerosol phase carbon disulfide photopolymer. Other techniques employed to characterize (CS)x include: AFM, SEM, electron and chemical ionization mass spectrometry, solid state 13 C NMR, Raman spectroscopy and XRD.;Carbon diselenide films were prepared by gas phase photolysis of CSe 2. Effective methods for synthesizing and collecting these films were not developed, although they had been previously observed. Elemental analysis found an approximate stoichiometry of (CSe1.4)x. FT-IR spectra suggest the CSe2 photopolymer may be similar in structure to (CS)x. Film thicknesses of 200 nm were measured by SEM. The morphological similarity to (CS)x may be suggestive of a similar bulk phase formation process. EPR studies show moderate intensity resonances indicative of selenium and carbon centered radicals. DSC scans found no free selenium present in the films.;Sulfur isotope fractionation studies were performed Using (13 CS2)x and (13CS)x and compared with values for (12CS2)x and (12CS)x. No isotope effect was observed for the (CS)x species prepared by photolysis of liquid phase CS 2, but a large sulfur isotope distribution was observed in ( 13CS2)x when compared with (12CS 2)x, which is prepared by gas phase photolysis. These result suggest that Franck-Condon and vibronic coupling effects on nonradiative decay and intersystem crossing rates for the lowest excited states of CS2 are responsible for the source of the mass-independent process, since a symmetry dependent processes can be ruled out.