Structure, spectroscopic properties, and photochemistry of the hydroxymethoxy radical

The hydroxymethoxy (HMO) radical is proposed to be the primary product of photodissociation of the atmospherically important hydroxymethyl hydroperoxide (HMHP). This transient species is still unknown and the present study provides theoretical predictions of properties, spectroscopy, and photochemistry of this radical for the first time. Structures, harmonic frequencies, vertical and vibrationally resolved absorption spectra are computed for several electronic states, using state-of-the-art ab initio electronic structure methods. The lowest excited state, absorbing in the mid to near infrared, seems to be the most promising candidate for spectroscopic identification of HMO. The electron affinity of 2.232 eV and the characteristic photodetachment spectrum is also predicted to be suitable for experimental investigations. By contrast, the B state absorbing around 3.5 eV is proposed to undergo fast photodissociation, forming CH(2)O and OH, and thus appears less useful for spectroscopic detection of HMO. However, the photodissociation may be important for the atmospheric chemistry of HMHP. Ionization of HMO will also lead to dissociation or rearrangement of the cation and will yield only unspecific spectra.