Journal of Physical Chemistry A, Vol.108, No.38, 7646-7652, 2004
Photodissociation of unsaturated alcohols. Energy distribution in the nascent OH radicals
The photodissociation of allyl and propargyl alcohols at 193 nm, which involves pi-pi* electronic transition and leads to the formation of OH, has been studied by using a laser photolysis-laser-induced fluorescence technique. The nascent OH radicals formed from both these molecules are found to be rotationally and vibrationally excited. The vibrational distributions are found to be similar, described by vibrational temperatures of 2070 +/- 380 and 2130 +/- 440 K for allyl and propargyl alcohols, respectively. The rotational temperatures of both nu" 0 and 1 levels of OH radicals from allyl alcohol are found to be almost the same, viz., 1960 +/- 150 and 1900 +/- 250 K, respectively, and close to the vibrational temperature. On the other hand, the rotational temperatures of OH radicals, 1760 +/- 130 K at the nu" = 0 level and 690 +/- 120 K at the nu" = 1 level, are very different from each other, in the case of propargyl alcohol. In both molecules, a significant part of the available energy is partitioned into the relative translational energy of the fragments, 118.4 +/- 22.2 and 148.0 +/- 23.0 kJ mol(-1) in allyl and propargyl alcohols, respectively. The results indicate a quantitative difference in the energy partitioning within the fragments of the two molecules, and only a hybrid model involving an exit barrier can explain the observations.