Abstract:
A detailed analytical investigation of the cadmium photosensitised decomposition of propane at 265°C and λ= 3261 Å has been made. The major products detected and estimated were methane, propylene, dimethylbutane (DMB), ethylene and hydrogen. Minor products detected were traces of ethane and isobutane. The major products were found to form initially at accelerated rates with time. (CH4/H2), (C3H6/H2) and (C2H4/CH4) ratios were found to decrease with conversion or time in a given run at a given reactant pressure, while (DMB/H2) ratio was found to increase. The ratio of the rate constants (k1/kb) of the reactions, viz., Cd(3P1)+ C3 H8→ CdH + i- C3H7(1) Cd(3P1)→ Cd(1S0)+hv(b) was found to be 3.30 × 102 dm3 mol–1 at zero cadmium concentration in the reaction vessel. If the radiative lifetime of Cd(3P1) be 2 × 10–6 s, then k1 becomes 1.68 × 108 dm3 mol–1 s–1, which gives 0.015 Å2 as the quenching cross section of propane per molecule, in agreement with the value of Steacie and LeRoy (i.e., 0.012 Å2). If (1/kb) be 1.0 × 10–4 s, as reported by Strausz et al., then k1 becomes 3.30 × 106 dm3 mol–1 s–1, which gives 0.000 29 Å2 as the quenching cross section. The disproportionation/combination rate constant ratios, (kd/kc), of isopropyl radicals at 265°C was found to be unity.
