Ultra-violet absorption spectrum of trichloro ethylene

Abstract

A system of bands starting at ca. 1686 Å is analyzed and shown to comprise at least two, probably three, electronic transitions. The strongest of these transitions has a vibrational pattern that is almost quantitatively identical with that of another transition whose origin is at 1553 Å. All the transitions referred to are Rydberg in nature. Those in the 1686 Å group are transitions to p Rydberg orbitals of an electron from an orbital that is primarily localized on the C atoms, is anti-symmetric with respect to the molecular plane, is CC bonding and to a lesser extent is C—Cl anti-bonding. The 1553 Å system represents a similar transition to an s or d Rydberg orbital. The vibrational structure shows that, compared with the ground state of the molecule, the Rydberg upper states and the ground state of the C₂Cl₃H⁺ ion have a weakened CC bond, slightly strengthened CCl bonds and slightly decreased ClCC angles. The data support the value 9.45 eV reported by Watanabe, Nakayama and Mottl for the first ionization potential.