Laser-induced fluorescence spectroscopy of biacetyl A 1Au(S1)–X 1Ag(S0))

The A 1Au(S1)–X 1Ag(S0) laser-induced fluorescence excitation spectrum of biacetyl has been observed under supersonic jet condition. Three weak bands have been observed at 22 182, 22 169 and 22 278 cm−1. Having considered the tunneling splitting of G01 and A01 bands, the band origin 000 is determined at 22 182 cm−1. The spectrum could be analyzed with three active modes: ν16(au) acetyl torsion, ν15(au) gearing methyl torsion and ν21(bu) antigearing methyl torsion. The observed fluorescence spectrum has been completely assigned. The fundamental frequency and anharmonicity constant of acetyl torsion mode are about 87.5 and 5.25 cm−1, respectively.