Infrared laser-induced decomposition of tert-butyl alcohol

Abstract

The decomposition of tert-butyl alcohol (2-methylpropan-2-ol) by pulsed infrared radiation from a TEA CO₂ laser has been examined, using the 10P30 line at 934.9 cm^–1. Over the pressure range 0.007–1,3 kPa the absorption cross-section increases with increasing pressure due to hole-filling by collisional rotational relaxation. Experiments on the decomposition were carried out at low total pressure (6.7 Pa) to minimise the effects of collisions during the pulse. The fluence range used was 3.3–6.4 J cm^–2. Under these conditions the only decomposition product detected was isobutene (2-methylpropene) generated in the reaction:

(CH ₃ ) ₃ COH →(CH ₃ ) ₂ CCH ₂ + H ₂ O

Addition of the diluent gases hexane and xenon reduced the extent of decomposition, and product yields from the diluted tert-butyl alcohol were compared with values calculated by assuming particular forms of the intermolecular energy distribution and by using RRKM rate constants. The comparison indicates that about half the irradiated molecules absorb the 10P30 radiation. The fraction of absorbing molecules deduced from the absorption measurements is considerably smaller than this, and reasons for the discrepancy are discussed.