A STUDY OF THE SINGLET-TRIPLET PERTURBATIONS IN THE (A)OVER-TILDE 1AUSTATE OF ACETYLENE BY HIGH-RESOLUTION ULTRAVIOLET SPECTROSCOPY

Laser-induced fluorescence spectra of the 3(0)3 K-0(1) and 3(0)4 K-0(1 ) vibronic bands of the A 1A(u) <-- X 1SIGMA(g)+ transition in acetyle ne have been recorded with a resolution of 18 MHz. Each rotational tra nsition consists of a group of lines due to coupling of the electronic ally excited singlet state with isoenergetic triplet states. Using the standard deconvolution procedure the singlet-triplet coupling element s and the density of coupled triplet states are derived for rotational levels up to J=4 in both bands. From the density of coupled triplet s tates it is concluded that the A 1A(u) state is perturbed by the T1 B- 3(2) state. Magnetic field measurements have shown that the predissoci ation of acetylene in the 4nu3' vibrational level of the A state is ca used by a coupling via the T1 B-3(2) state with predissociating vibrat ional levels of the electronic ground state.