THE HYDROXYL RADICAL REACTION-RATE CONSTANTS AND ATMOSPHERIC REACTION-PRODUCTS OF 3 SILOXANES

The relative rate technique has been used to measure the hydroxyl radi cal (OH) reaction rate constant of hexamethyldisiloxane (MM, (CH3)(3)S i-O-Si(CH3)(3)), octamethyltrisiloxane (MDM, (CH3)(3)Si-O-Si(CH3)(2)-O -Si(CH3)(3)), and decamethyltetrasiloxane (MD2M, CH3)(3)Si-O-Si(CH3)(2 )-O-Si(CH3)(2)-O-Si(CH3)(3)). Hexamethyldisiloxane, octamethyltrisilox ane, and decamethyltetrasiloxane react with OH with bimolecular rate c onstants of 1.32 +/- 0.05 x 10(-12) cm(3)molecule(-1)s(-1). 1.83 +/- 0 .09 x 10(-12) cm(3) molecule(-1)s(-1), and 2.66 +/- 0.13 x 10(-12) cm( 3)molecule(-1)s(-1), respectively. Investigation of the OH + siloxane reaction products yielded trimethylsilanol, pentamethyldisiloxanol, he ptamethyltetrasiloxanol, hexamethylcyclotrisiloxane, octamethylcyclote trasiloxane, and other compounds. Several of these products have not b een reported before because these siloxanes and the proposed,reaction mechanisms yielding these products are complicated. Some unusual cycli c siloxane products were observed and their formation pathways are dis cussed in light of current understanding of siloxane atmospheric chemi stry. (C) 1997 John Wiley C Sons, inc.