FOURIER-TRANSFORM INFRARED-EMISSION STUDY OF THE MECHANISM AND DYNAMICS OF HOI FORMED IN THE REACTION OF ALKYL IODIDES WITH O(P-3)

Vibrationally excited hypoiodous acid (HOI) is observed as a product i n the reaction of alkyl iodides with O(P-3). Fourier transform infrare d emission techniques are used to detect the excited nu(1), OH, stretc h of the HOI product, to determine the mechanism of HOI production, an d to measure the vibrational product state distributions. The HOI prod uct is formed by O atom reaction with two-carbon and larger straight o r branched chain alkyl iodides and cyclic alkyl iodides, e.g., C2H5I, n-C3H7I, i-C3H7I, (CH3)(3)CI, n-C6H13I, and c-C6H11I, but not with CH3 I. Experiments with selectively deuterated ethyl iodides provide direc t evidence that HOI is formed in a beta-elimination mechanism involvin g a five-membered ring transition state. The O atom attacks the iodine and then abstracts a hydrogen from the beta carbon during the lifetim e of the complex. Time-resolved experiments allow the extraction of na scent vibrational state distributions for the nu(1) stretch of HOI (up silon=1:upsilon=2:upsilon=3) using different alkyl iodides and assumin g the radiative rates are given by A(nu-->nu-1=upsilon A?(1-->0): C2H5 I, 0.53(4):0.39(3):0.08(3); n-C3H7I, 0.61(6):0.34(5):0.05(2); and i-C3 H7I, 0.54(6):0.38(4):0.08(3). These distributions are nonstatistical w ith the upsilon=2 states having only slightly less population than tho se with upsilon=1. For product molecules with up to three quanta of vl excitation, more than 50% of the reaction exothermicity is deposited into the OH stretch. (C) 1997 American Institute of Physics.