RESONANCE RAMAN-SCATTERING IN PHOTODISSOCIATING HALOMETHANES

Gas-phase resonance Raman spectra of the halomethanes CH3I, CH2ICl and CH2I2 were recorded with excitation wavelengths of an argon ion laser between 275.4 and 363.8 nm. The 275.4 nm laser line is resonant with the A-band absorption transition of the molecules CH3I and CH2ICl and was used for Raman excitation. Resonance Raman spectra of these two mo lecules are then dominated by an overtone progression of the resonance enhanced C-I stretching mode and weak combination bands. The structur e of the resonantly enhanced vibrational bands 3(1)-3(4) of CH3I are i nterpreted in terms of hot bands and rotational transitions in symmetr ic top molecules. The spectra of this mode (3(1)-3(4)) were simulated applying a model for linear and for non-linear symmetric top molecules . For CH2I2, which has four absorption maxima between 230 and 370 nm, further excitation wavelengths of an argon ion laser (335.1, 351.1 and 363.8 nm) were used to record resonance Raman spectra. All these spec tra show several overtones and combination bands of the symmetric and antisymmetric CI2 stretching modes v(3) and v(9). (C) 1997 by John Wil ey & Sons, Ltd.