Mercury photosensitization of toluene vapor and aerosol formation

Abstract

Abstract The triplet-mercury photosensitized decomposition of toluene vapor was performed at 298 K to determine the nature of the aerosols formed. The major product was bibenzyl, which was identified by gas chromatography—mass spectrometry, Fourier transform IR spectroscopy (FTIR) and 13 C and 1 H nuclear magnetic resonance spectroscopy, and its quantum yield was 1.05 × 10 −2 . Other products identified included methane, benzene and dimeric species. Aerosols were analyzed in situ by FTIR spectrometry and their FTIR spectra shown to correspond to bibenzyl. The rates of aerosol formation at different substrate pressures were studied using a laser light extinction photometer and shown to correlate linearly with the rate of bibenzyl formation. The average aerosol particle radii determined from differential settling measurements were 0.23, 0.30, and 0.43 μm at toluene pressures of 10 Torr, 15 Torr and 20 Torr respectively. Scanning electron microscopy measurements corroborated the particle sizes deduced from the light extinction measurements. Finally, ab initio molecular orbital calculations using the 3-21G basis set found Hartree—Fock energies of the 1 A′ and 3 A′ states of toluene and the benzyl radical plus hydrogen atom, anticipated dissociation products, to be −268.24022 a.u., −268.13720 a.u., and −268.13738 a.u. respectively. The benzene ring is significantly distorted in the triplet state, suggesting that considerable vibrational excitation occurs upon intersystem crossing. The benzyl radical is planar, as expected. Optimized geometries are reported.