The absorption spectrum of trans-diimide (N2H2) in the vacuum ultraviolet region

The vacuum ultraviolet absorption spectrum of trans-diimide (N2H2) in the gas phase has been re-examined between 1800 and 1300 A, using diimide prepared by the thermal decomposition of sodium tosylhydrazide. Two band systems were observed, designated and , with origins at 1727 and 1473 A, which have been assigned to the Rydberg transitions 3pπ(bu) ← n+ and 4pπ(bu) ← n+ respectively. Both systems show long progressions in v2′, the N—N—H symmetric bending frequency, and short progressions in v3′, the symmetric N—N stretching frequency.The system has well-resolved rotational J type structure in some bands, and the rotational analysis showed that the ground state is a totally symmetric singlet state of C2h symmetry (planar trans-N2H2 isomer), and that the system arises from a 1Bu ← 1Ag transition. Rotational constants obtained for the 0–0 band of the -state were A = 15.63, B = 1.32, and C = 1.22 cm−1, and the values of rH−N = 1.028 A, rH−N = 1.167 A, and were estimated from them assuming a planar trans confor...