COLLISIONLESS EXCITATION OF NH3 MOLECULES VIA ONE-PHOTON AND 2-PHOTON TRANSITIONS BY MULTIMODE RADIATION OF TEA CO2-LASER

The excitation of ammonia by 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 (NH3)-N-14 molecules in the 2-nu-2 a(1, 1) <-- a(1, 1) transition by the 10P(24) CO2-laser line, the frequency offset of which is approximately 0.02 cm-1, can be described well by modelling the laser radiation as a broadband chaotic field. The experimental results of one-photon excitation in (NH3)-N-14 and (NH3)-N-15 [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.