Rotationally resolved laser-induced fluorescence of biacetyl in A 1Au–X 1Ag

Abstract

Laser-induced fluorescence of jet-cooled biacetyl was recorded in the region of 22 177–22 277 cm−1 with a resolution of 0.012 cm−1. Three bands, 000, 1501, and 2101 with transitions J″⩽3 were observed and analyzed. For the 000 band, E2–E1 and G–G subbands were observed. However, only c-type transitions, ΔKa=odd, ΔKc=even, were observed. Another kind of transition, d-type (ΔKa=even, ΔKc=even), which is allowed by selection rules, was not observed. For the 1501 band, two subbands E3–E3 and G–G were observed. The E3–E3 subband can be described by the rigid rotor model, and it contains only ΔKa=odd, ΔKc=even transitions. On the other hand, the G–G subband cannot be even approximately described by the rigid rotor model. It is dominated by c-type transitions. In addition, a/b-type and d-type transitions were all observed, though the intensities are small. For the 2101 band, E2–E1, G–G, and A3–A1 subbands were observed. The E2–E1, G–G subbands contain all the possible types of transitions, i.e., a/b-and c/d-type transitions. However, the A3–A1 subband has ΔKa=odd, ΔKc=even transitions only. The band origin, rotational constants, and the splitting due to the tunneling in these three bands was accurately measured. Relatively large vibronic transition intensities were observed in both the 1501 and 2101 bands.