Double optical-IR resonance effect for the single rotational level of the V12K12 vibronic transition of C2H2

DOIRR spectrum was recorded in C2H2 for triplet levels coupled by intramolecular interactions to levels of an adjacent A 1Au singlet state, excited into individual rotational level of the 32 vibronic state. The spectrum was recorded for the V12K12, J′ = 4 level. The spectrum fitting and line assignment were done using a statistical model. The rotational constant B determined as a spectral fitting parameter is ca. 0.43 cm−1. Time-resolved measurements were carried out for DOIRR spectral line located at 1538 G. It was found that at intermediate IR power levels, the fluorescence decay is biexponential, due to reversibility of the S-T conversion.