LAUSR

The ultraviolet (UV) absorption spectrum of the simplest deuterated Criegee intermediate CD2OO has been measured and compared with that of CH2OO. While the UV spectra of CH2OO and CD2OO are similar in the overall shape, distinctive oscillatory structures at the long wavelength side of the absorption band show clear effect of isotopic substitution. The average spacing between the vibrational peaks decreases from 606 cm−1 for CH2OO to 528 cm−1 for CD2OO. This large isotope effect cannot be explained by one-dimensional model along the dissociative O−O bond. Instead, vibrational modes involving motions of the H-atoms are expected to be responsible for the observed oscillatory structure. This isotope effect offers a stringent test for theoretical investigations on the absorption spectrum and excited-state dynamics of the simplest Criegee intermediate.