Wavelength dependent photodissociation of CH3OOH

Methyl hydroperoxide, CH3OOH, has been synthesised with >99.5% purity, confirmed using UV absorption spectroscopy and high-pressure liquid chromatography (HPLC) followed by post-column derivatisation. The UV absorption cross-section for CH3OOH was measured and for <325 nm was in good agreement with the literature. Laser-flash photolysis combined with laser-induced fluorescence (LIF) spectroscopy has been used to measure both OH and CH3O photofragments following the photolysis of CH3OOH in the wavelength range 223-355 nm. Using the previously measured unity quantum yield for OH at 248 nm as a reference, the LIF signals immediately following photolysis were used to measure wavelength dependent quantum yields for OH and CH3O, taking into account changes in laser pulse energy and absorption cross-section. The quantum yields for both species were unity within experimental error. The rate coefficient for the reaction of OH with CH3OOH (R1a) to generate CH3O2 + H2O products was measured at 295 K to be k(R1a) = (9.0 ± 0.2) × 10−12 cm3 molecule−1 s−1, considerably higher (by about a factor of two) than previous values measured by Vaghjiani and Ravishankara [G.L. Vaghjiani, A.R. Ravishankara, J. Phys. Chem. 93 (1989) 1948-1959] and Niki et al. [H. Niki, P.D. Maker, C.M. Savage, L.P. Breitenbach, J. Phys. Chem. 87 (1983) 2190-2193].