AN EMISSION SPECTRUM OF THE DIACETYLENE ION: A STUDY OF SCHÜLER'S "T" SPECTRUM UNDER HIGH RESOLUTION

Abstract

Schüler and Reinebeck have described a new spectrum which was observed in a discharge through a mixture of an inert gas and the vapor of any of a number of organic compounds. This spectrum was labelled "T". Further experiments by the authors provided evidence that the carrier of the "T" spectrum was the diacetylene molecule. The "T" spectrum has now been reinvestigated using both normal and fully deuterated diacetylenes in a helium discharge and photographed on grating instruments with very high resolving powers. Previous vibrational assignments were extended, and the rotational structure was completely analyzed in four bands. The results, together with other evidence, show that the carrier of the "T" spectrum is the diacetylene ion, C₄H₂⁺. The vibrational and rotational constants differ but little from those of the diacetylene ground state. The spectrum involves a transition between the first excited state A²Π_u(i) and the ground state X²Π_g(i) of the ion and is analogous in detail to the well-known Fox, Duffendack, and Barker system of CO₂⁺.