Rotation-Vibration Spectra of Diatomic and Simple Polyatomic Molecules with Long Absorbing Paths VII. The Spectrum of Dideuteroacetylene (C2D2) in the Photographic Infrared

Abstract

Twelve absorption bands of C2D2 have been observed in the photographic infrared. Eleven of these bands show simple P and R branches with intensity alternation, i.e., they are Σu+—Σg+ bands while one band, without intensity alternation, is a difference band of type Π—Π. From the positions of the bands some of the vibrational constants ωi0 and xik are determined. In addition, from the rotational fine structure, the rotational constants B[v] and D[v] are determined. For B[0] the value 0.84787 cm−1 is obtained. The αi values are α1=+0.00578, α2=+0.00302, α3=+0.00455, α4=−0.00120, α5=−0.0026 cm−1. From the αi and B[0] one obtains Be=0.85075 cm−1. Combining Be(C2D2) with Be(C2H2) yields, for the internuclear distances in the acetylene molecule, re(C≡C)=1.2010×10−8 and re(C–H)=1.0637×10−8 cm in very satisfactory agreement with the values previously obtained from Be(C2HD) and Be(C2H2). Evidence for l-type doubling in C2D2 is given and approximate values for the l-type doubling constants q4 and q5 are obtained.