Free Radicals by Mass Spectrometry: Xxii. Primary Decomposition Steps in the Mercury-Photosensitized Decomposition of Methanol and Dimethyl Ether

Abstract

The Hg 3P1 photosensitized decomposition of methanol at low pressures proceeds mainly by a dissociation into CHBO radicals and H atoms. No formation of CHzOH radicals is observed. A s~lbsidiary reaction to form CH3 and OH may also be a primary step. Formation of CHzOH radicals at higher pressures is attributed to an abstraction reaction of CH30 with CHxOI-I.Two primary modes of dissociation are found to occur for dimethyl ether:The relative probabilities of occurrence at low pressures are ~4 5 7~ and ~5 0 % , respectively. The possibility that the second reaction proceeds by formation of an excited molecule is discussed.

PRIMARY METHOXY RADICAL FORMATION IN THE REACTION OF METHANOL VAPOR WITH Hg 6(3P1) ATOMS

“…Thus we co~lclude that reaction [5] cannot be more than five per cent of the priinary reaction, and that it is inore lilrely to be roughly two per cent of it. These conclusioils would support the suggestion made by Pottie et al (9) that CH3 formation arises froin atomic cracking:…”

“…explaiil the appearance of N20 and 1-120 in systems containing EI atoms and NO. The analogous reaction t o [9], for ethoxy radicals has been postulated by Levy (13) for the thermal decoinposition of ethyl nitrite. T h e reaction should be highly exothermic.…”

Primary process(es) in the mercury-photosensitized decomposition of dimethyl ether at 2537 Å

“…In [I] the excited DME molecule is deactivated by collision at high pressure, but in [2] its excess energy is involved in the rupture of the weakest bond. The latter process will predominate at low pressures but the two modes of deactivation will be in competition over a considerable pressure range.…”

“…Lossing et al (2) did not exclude the formation of excited DME molecules in the primary process and this reaction may be included as one of the Can. J. Chem.…”

“…-Paper presented at the 50th CIC Conference, Toronto, June 4-7, 1967. nonoccurrence of the mode of dissociation involving a C-0 split in the 28 to 500 Torr region was interpreted by Lossing et al (2) in terms of an excited ether molecule which could be completely deactivated at these pressures and hence not be able to dissociate.…”