Ultraviolet laser multiphoton excitation of CH2I2

Laser multiphoton excitation of CH2I2 has been studied at 248 nm (KrF laser) and 193 nm (ArF laser). Intense photofragment fluorescence is observed from CH(A2Δ), with weaker fluorescence from CH(B2Σ–) and CH(C2Σ+), following excitation at both wavelengths. The rotational structure in the CH(A2Δ→X2Π) system has been partially resolved and it is shown that this radical is formed with a high rotational temperature (ca. 3000 K) when CH2I2 is excited at 248 nm. Fluorescence from I(5p46s2P3/2) and the F1Σ+u, D1Σ+u and D′3Π2g states of I2 is also observed and carbon atoms in the 21D2 and 21S0 states are detected by laser-induced fluorescence. Mechanisms which account for the formation of these photofragments involving both multiphoton and multiple-photon excitation are discussed and the results are compared with those for single-photon excitation of CH2I2 in the near and vacuum ultraviolet.