Diode laser detection of iodine atom hyperfine transitions during and after infrared multiphoton excitation and dissociation of CF₃I with short pulse CO₂ lasers

The iodine atom concentration has been measured by time-resolve absorption spectroscopy for all hyperfine levels on the I(²P _{3 2})→I(²P _{1 2})) transition during and after the multiphoton excitation of CF₃I, using a tunable diode laser in the near infrared at 1.3 μm. The experiments have been performed under collision free conditions with a time resolution of about 1 ns. Using CO₂ laser pulses of different temporal shape, the nonlinear intensity dependence of the multiphoton excitation process and the previously measured steady state rate constants have been confirmed. Detection at different hyperfine transistion frequencies and charging the relative orientation of the polarization of the pump and probe laser showed statistical behaviour for the population of the hyperfine levels and for the orientation of the iodine atoms. Using CO₂ laser pulses of specially tailored temporal shape the theoretically predicted intensity fall-off for the steady state rate constant has been found experimentally.