LASER-INDUCED VIBRATION-ROTATION FLUORESCENCE AND INFRARED FORBIDDEN TRANSITIONS IN ACETYLENE

Laser induced fluorescence method has been used to study highly excite d vibrational overtones in acetylene. A sample cell has been placed in side a Ti:Sapphire ring laser cavity and the total fluorescence collec ted by a parabolic mirror has been dispersed by a high-resolution FTIR spectrometer. The laser has pumped specific rotational slates of the CH stretching vibrational overtone state nu(1)+3 nu(3)(Sigma(u)(+)) an d transitions to the symmetric state nu(1)+2 nu(3)(Sigma(g)(+)) have b een observed. The observations allow determining both the vibrational term value and the rotational constant of the symmetric state, which i s not accessible from the ground vibrational state by one-photon absor ption. The parameters obtained sire in excellent agreement with simple local mode predictions. (C) 1997 American Institute of Physics.