G.C.G. Wachewsky, R. Horansky, and V. Vaida (J. Phys. Chem. 100, 11559 (1996)) examined the UV absorption spectrum ofCH3I, a species of interest in connection with stratospheric ozone chemistry. They found the integrated absorption coefficient to be dependent on temperature and pressure to an extent inconsistent with internal structural changes in isolated CH3I molecules; they explained the changes as due to dimerization of a substantial fraction of the CH), a process that would naturally be pressure and temperature dependent.
(a) Compute the integrated absorption coefficient over a triangular lineshape in the range 31250 to 34483 cm-1 and a maximal molar absorption coefficient of 150 dm3 mol-l cm3 at 31 250 cm-1.
(b) Suppose 1 per cent of the CH) units in a sample at 2.4 Torr and 373 K exist as dimers. Compute the absorbance expected at 31250 cm3 in a sample cell of length 12.0 cm.
(c) Suppose 18 per cent of the CH3I units in a sample at 100 Torr and 373 K exists as dimers. Compute the absorbance expected at 31250 cm-1 in a sample cell of length 12.0 cm; compute the molar absorption coefficient that would be inferred from this absorbance if dimerization was not considered.