The e.p.r. spectrum of vibrationally excited hydroxyl radicals

The e. p. r. spectrum of vibrationally excited hydroxyl radicals in levels v = 1, 2, 3 and 4 of the 2II3/2 ground state has been observed in the reaction between hydrogen atoms and ozone in the gas phase. Although the variation of ∧-doubling with vibrational energy superficially agrees well with the ‘pure precession’ model of Van Vleck, there is clear evidence that the matrix element decreases considerably with increasing internuclear distance. The form of the decrease in the hyperfine coupling constants with increasing vibrational energy agrees well with that deduced from Kayama’s theoretical calculations.