The magnetic circular dichroism (MCD) spectrum of gas phase acetylene has been studied in the spectral region 320-140 nm. No MCD signal was detected in the region of the first transition. The observation of irregular MCD bands beginning at 185 nm confirm assignment of this latter band as the 0-0 band of the second transition. The discrete and relatively narrow bands in the region 155-140 nm exhibit pure A-term character, lending unambiguous confirmation to the assignment of 1Πu for the state. The observed absorption spectrum in this region is interpreted as consisting of two non-interacting systems, one involving the 1Πu Rydberg state and the other, a broad continuous background, cannot be assigned. It is however suggested that it may be due to the 1Σu+ state of the π → π* excited configuration.
Bibliographical noteFunding Information:
l Work supported by a -grant of the National Institutes of Hnlth. * Permanent address: 13epartment of Chemistry, Bar-llan University, Ramat-Can, Israel.