Infrared-microwave double-resonance probing of the population-depopulaton of rotational states in the NO2 molecule

A 10.6-μm CO₂ laser operating over a power range 5 ≤ p ≤ 135 watts was used to pump some select vibrational transitions in the NO₂ molecule while monitoring the rotational transitions (9_1,9 → 10_0,10), (23_2,22 → 24_2,23), and (40_2,38 → 39_3,37) in the (0, 0, 0) vibrational level and the (8_0,8 → 7_1,7) rotational transition in the (0, 1, 0) vibrational level. These rotational transitions were monitored by microwave probing to determine how the population of states in the rotational manifolds was being altered by the laser. Coincidences between some components of the ν₃-ν₂ band of NO₂ and the CO₂ infrared laser lines in the 10-μm region appeared to be responsible for the strong interaction between the continuous laser beams and the molecular states. Characteristic rate curves for population-depopulation changes in the chosen rotational levels listed above were found for various power levels from the laser pump. Rate coefficients for intensity decay for various laser powers were calculated from experimental data and are presented.