Photolysis of Nitromethane and of Methyl Nitrite in an Argon Matrix; Infrared Detection of Nitroxyl, HNO

Abstract

The photolysis of nitromethane in solid argon at 20°K gives methyl nitrite. All other products can be explained in terms of the secondary photolysis of methyl nitrite. This work provides a definitive basis for segregating the vibrational frequencies of the cis- and trans-isomers of methyl nitrite. The primary products of photolysis of methyl nitrite under these conditions are formaldehyde and nitroxyl, HNO. The identification of HNO, detected by its infrared spectrum for the first time, is confirmed by the band shifts occurring upon deuteration. The vibrational frequencies of HNO (1570 and 1110 cm-1) and DNO (1560 and 822 cm-1) correspond to a bent molecule with a double bond between the nitrogen and oxygen atoms, thus supporting the structure HNO over the possible arrangement HON. The bending force constant, 0.67·10-11 dyne-cm, suggests that the HNO angle is near 110°, larger than the earlier estimate of 102° based on electronic spectra.