Ultra-violet absorption spectrum of cis-1,2-dichloro ethylene

Abstract

The spectrum is described and its interpretation discussed. Transitions whose origins are taken to lie at 1674, 1640, 1518 and around 1430 Å have, qualitatively and quantitatively, very similar vibrational patterns. Thence it is argued that all the transitions mentioned are Rydberg in type and associated with the same (the first) ionization potential. Relative to the ground state of the neutral molecule, each Rydberg state and the ground state of the positive ion have a reduced CC stretching frequency and an increased CCl stretching frequency. From this, and in accord with simple theoretical considerations, the upper states of the Rydberg transitions and the ground state of the positive ion are all deduced to have, relative to the ground state of the neutral molecule, an increased CC length and a decreased CCl length. The value 9.66 eV previously found for the first ionization potential is confirmed.