Abstract
Spectra of vibronic bands 15 0 1 , 14 0 1 15 0 1 of S 1 (n, π * )-S 0 of d 4 -acetaldehyde in a supersonic jet are recorded and analyzed. The fitted rotational parameters A, B and C of vibrational levels 15 1 and 14 1 15 1 are 1.040(4), 0.280(5) and 0.249(5) cm -1 and 1.038(5), 0.282(5) and 0.250(5) cm -1 , respectively. The rotational structure of these two vibronic bands consists of a-, b- and c-type transitions; according to spectral intensity of these band types we tentatively assign the 15 1 level to lie below the level 14 1 15 1 . Hence, the term value of 15 1 of S 1 is determined to be 145.35 cm -1 . The lifetimes of low rotational states of the 0 0 , 15 1 and 14 1 15 2 of S 1 (n, π * ) h 4 -acetaldehyde are measured to be in the range of 171-206, 177-262 and 164-191 ns, respectively. The average lifetime of rotational states of 15 1 is longer than those of levels 0 0 and 14 1 15 2 indicates that this torsional level might be perturbed by some nearby triplet state T 1 .