Collisionless excitation of NH3 molecules via one- and two-photon transitions by multimode radiation of TEA CO2 laser

The excitation of ammonia via one- and two-photon transitions by TEA CO2-laser radiation has been studied under collisionless conditions. It has been shown that the experimental results of two-photon excitation of 14NH3 molecule in the 2 (nu) 2 a(1, 1) $IMP a(1, 1) transition by the 10P(24) CO2-laser line, the frequency offset of which is approximately equals 0.02 cm-1, can be described well by modeling the laser radiation as a broadband chaotic field. The experimental results of one-photon excitation in 14NH3 and 15NH3,4 with the offset values exceeding the CO2- laser linewidth, can be also described well with the use of a chaotic field with a continuous spectrum. In the case of a nearly exact one-photon resonance, however, the excitation efficiency of molecules depends critically on the real mode structure of the CO2-laser radiation.