OH-Stretch Vibrational Spectroscopy of Hydroxymethyl Hydroperoxide

Abstract

We report measurement and analysis of the photodissociation spectrum of hydroxymethyl hydroperoxide (HOCH 2 OOH) and its partially deuterated analogue, HOCD 2 OOH, in the OH-stretching region. Spectra are obtained by Fourier transform infrared spectroscopy in the 1ν OH and 2ν OH regions, and by laser induced fluorescence detection of the OH fragment produced from dissociation of HOCH 2 OOH initiated by excitation of the 4ν OH and 5ν OH overtone regions (action spectroscopy). A one-dimensional local-mode model of each OH chromophore is used with ab initio calculated OH-stretching potential energy and dipole moment curves at the coupled-cluster level of theory. Major features in the observed absorption and photodissociation spectra are explained by our local-mode model. In the 4ν OH region, explanation of the photodissocation spectrum requires a nonuniform quantum yield, which is estimated by assuming statistical energy distribution in the excited state. Based on the estimated dissociation threshold, overtone photodissociation is not expected to significantly influence the atmospheric lifetime of hydroxymethyl hydroperoxide.

Vibrational overtone initiated unimolecular dissociation of HOCH2OOH and HOCD2OOH: Evidence for mode selective behavior

“…2͑a͒ are associated with the two zeroth order OH stretching motions in the molecule, with the feature at lower frequency ͑13 330 cm −1 ͒ corresponding to the peroxide OH stretch and the one at higher frequency ͑13 580 cm −1 ͒ to the alcohol OH stretch. 17 As D 0 for breaking the peroxide O-O bond in HMHP is estimated to be ϳ13 950 cm −1 ͑ϳ39.9 kcal/ mole͒, 17 spectral features associated with the 4 OH bands lie close to the dissociation threshold. Hence, in this spectral region the observed spectral intensities are influenced not only by their absorption cross sections but also through variations in dissociation quantum yield with available energy.…”

“…We generate HMHP and its deuterated analog ͑HMHP-d 2 ͒ in a manner similar to that described in our earlier work. 17 After synthesis, the resulting liquid HMHP sample is immediately placed in a round bottom flask, situated inside a sturdy Plexiglass housing, for use during the experiments. The Plexiglass box serves as a barrier against potential peroxide explosions.…”

“…This extended pumping minimizes contaminants such as H 2 O, HCOOH, and H 2 O 2 typically present in the sample as noted in our earlier study. 17 The sample pressure in the photolysis cell is maintained around 60-80 mTorr in these measurements. Laser light for excitation in the region of the third ͑4 OH ͒ and fourth OH stretching overtones ͑5 OH ͒ are generated by a dye laser ͑Con-tinuum: ND60͒ pumped by the second harmonic of a Nd:YAG ͑yttrium aluminum garnet͒ laser ͑Continuum: NY82-20͒.…”

“…2͑a͒-2͑d͒ for reference. 17 These spectra were generated by monitoring yields of nascent OH͑v =0, 2 ⌸ 3/2 ͒ fragments, respectively, in the N = 1 and N = 3 rotational states as the wavelength of the vibrational excitation laser is scanned over the region of the 4 OH and 5 OH bands. One dimensional spectral simulation using an ab initio dipole surface and potential along the OH stretching coordinate ͑CCSD͑T͒/aug'-cc-pVTZ͒ suggest that the two most prominent features appearing in the 4 OH spectrum shown in Fig.…”

“…Ab initio calculations also reveal that there are three stable conformers of HMHP. 17 By including corrections for zeropoint vibrational energy, the conformers are predicted to have relative energies of 0, 13, and 215 cm −1 . The OH stretching frequencies and anharmonicities of these conformers are very similar to one another and apparently in the 4 OH region, their bands overlap to a large extent, so they are not resolved in these room temperature experiments.…”