Ultra-violet absorption spectrum of tetrachlorohylene

Abstract

Four banded absorption systems of the C₂Cl₄ molecule are described. The vibrational patterns of all four are almost identical, qualitatively and quantitatively; from which it is deduced that all four transitions are Rydberg in type. They belong to a Rydberg series converging to a first ionization potential at 9.33 eV. The vibrational patterns are due to excitation of the three fundamental vibrations, ν^′₁ν^′₂ and ν^′₃ of the upper states, and to be in accord with simple theory based on symmetry considerations. The qualitative conclusions are that, relative to the ground state of C₂Cl₄, the upper states (and the ground state of the C₂Cl⁺₄ ion) have an increased CC length, a less marked decrease in CCl length and a small increase in [graphic omitted] angle. These qualitative conclusions are then made quantitative by an application of the Franck-Condon principle; the increase in CC length is 0.11 ± 0.01 Å, the decrease in CCl length is 0.03 ± 0.015 Å and the increase in [graphic omitted] angle is 3 ± 1°.