Abstract
UV photochemistries of benzene, alkylbenzenes, and olefins are described from a new point off view: hot molecule mechanism. Hot molecule (denoted as S0**) is a highly excited vibrational state in the ground electronic state. The primary process of these molecules irradiated with Ar F laser light (193.2 nm) is internal conversion to the ground state in the gas phase and S0**forms. The equivalent vibrational temperatures of S0**are very high 2000-4000K. Subsequent reactions are found to be similar to those driven by thermal energy.
Hot molecule (S0**) can be an intermediate of UV multiphoton dissociation. S0** shows strong absorption in the U V region and hence efficiently absorbs a second photon which causes dissociation. Radical fragmentations are major reactions for this new multiphoton chemistry.
