FRANCK-CONDON DOMINATED CHEMISTRY - DISSOCIATIONS OF SILICON-CENTEREDRADICALS PREPARED BY FEMTOSECOND REDUCTION OF THEIR CATIONS IN THE GAS-PHASE

The dimethylhydroxysilyl radical, (CH3)(2)(SiOH)-O-., (1) is generated in the gas phase by collisional neutralization of its cation 1(+). Ra dical 1 undergoes extensive dissociation by C-Si bond cleavage dependi ng on the internal energy of the precursor ion 1(+). A small fraction of stable 1 is obtained from vibrationally excited 1(+). Significant f ractions of stable deuterio analogues of 1, (CD3)(2)(SiOH)-O-. and (CH 3)(2)(SiOD)-O-., are formed from their corresponding gas-phase cations . Stable CH3SiOH molecules and (H2SiOH)-O-., [CH3,SiO](.), and (CH3)(3 )Si-. radicals are also formed by collisional neutralization of their cations. Collisional reionization of gas-phase 2-silapropan-2-one resu lts in extensive dissociation of its cation radical. MP4(SDTQ)/6-31+-G (d) calculations predict large Franck-Condon effects in the vertical r eduction of 1(+) that deposits up to 229 kJ mol(-1) in the radical for med. Isodesmic and charge-transfer reactions are used to estimate the heat of formation of 1 as -254 kJ mol-l, and its adiabatic ionization energy as 6.25 eV. The dissociation energies of the O-H and C-Si bonds in 1 are calculated as 166 and 195 kJ mol(-1), respectively.