Vibrational-Rotational Spectra of Normal Acetylene and Doubly Deuterated Acetylene: Experimental and Computational Studies

Abstract

Two molecules of astrophysical interest, normal acetylene (C 2 H 2 ) and deuterated acetylene (C 2 D 2 ) were synthesized and their spectra have been recorded using Fourier Transform Interferometer (FTIR) at low resolution between 400 and 4000 cm -1 . Vibrational bands and frequencies of interest have been identified and analyzed. Experimental excited rotational constants (B) and ground rotational constant (B) respectively for C 2 H 2 as 35.4172±0.0036 and 35.3348±0.036 GHz while for C 2 D 2 as 25.3820±0.0045 and 25.2771±0.0045 GHz have been determined. At the MP2 level of theory with the aug-cc-pvtz basis set, we calculated the equilibrium rotational constant of C 2 H 2 to be 35.1819 GHz and 25.2495 GHz for C 2 D 2 . While, at CCSD(T) level of theory with the same basis set, rotational constant value of 35.0892 and 25.2574 GHz were calculated for C 2 H 2 and C 2 D 2 respectively. The experimental C-H and C-C bond lengths of acetylene were calculated to be 1.08653 Å and 1.18983Å respectively. The importance and the astrophysical relevance of these results are discussed.