KINETICS OF THE GAS-PHASE REACTIONS OF A SERIES OF ORGANOSILICON COMPOUNDS WITH OH AND NO3 RADICALS AND O-3 AT 297 +/- 2-K

Rate constants for the gas-phase reactions of tetramethylsilane, hexamethyldisiloxane, hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, and decamethylcyclopentasiloxane with OH and NO3 radicals and O3 have been determined at 297 +/- 2 K. The rate constants obtained for these OH radical, NO3 radical, and O3 reactions (in cm3 molecule-1 s-1 units), respectively, were as follows: for tetramethylsilane, 1.00 x 10(-12), < 8 x 10(-17), and < 7 x 10(-21); for hexamethyldisiloxane, 1.38 x 10(-12), < 8 x 10(-17), and < 7 x 10(-21); for hexamethylcyclotrisiloxane, 5.2 x 10(-13), < 2 x 10(-16), and < 3 x 10(-20), for octamethylcyclotetrasiloxane, 1.01 x 10(-12), < 2 x 10(-16), and < 3 x 10(-20); and for decamethylcyclopentasiloxane, 1.55 x 10(-12), < 3 x 10(-16), and < 3 x 10(-20). The NO3 radical and O3 reactions are calculated to be of no importance as tropospheric removal processes for these compounds. The calculated lifetimes of these volatile organosilicon compounds in the troposphere due to chemical reaction with the OH radical range from approximately 10 days for decamethylcyclopentasiloxane to approximately 30 days for hexamethylcyclotrisiloxane.