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 in the reaction of alkyl iodides with O(P-3). Fourier transform infrared emission techniques are used to detect the excited nu(1), OH, stretch of the HOI product, to determine the mechanism of HOI production, and to measure the vibrational product state distributions. The HOI product is formed by O atom reaction with two-carbon and larger straight or 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 CH3I. Experiments with selectively deuterated ethyl iodides provide direct evidence that HOI is formed in a beta-elimination mechanism involving a five-membered ring transition state. The O atom attacks the iodine and then abstracts a hydrogen from the beta carbon during the lifetime of the complex. Time-resolved experiments allow the extraction of nascent vibrational state distributions for the nu(1) stretch of HOI (upsilon=1:upsilon=2:upsilon=3) using different alkyl iodides and assuming the radiative rates are given by A(nu-->nu-1=upsilon A?(1-->0): C2H5I, 0.53(4):0.39(3):0.08(3); n-C3H7I, 0.61(6):0.34(5):0.05(2); and i-C3H7I, 0.54(6):0.38(4):0.08(3). These distributions are nonstatistical with the upsilon=2 states having only slightly less population than those 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.