Microwave Spectrum and Molecular Structure of Methylchloroacetylene

Abstract

The J = 6←5 rotational transitions have been observed for 10 isotopic species of CH₃CCCl, including four of the fully deuterated molecule. The values for D_J were calculated from the force constants of the molecule, and are tabulated with the resulting values for B₀. The structural parameters giving the best fit to the 10 moments of inertia I_B are: r₀(C–Cl) = 1.6371 A, r₀(C≡C) = 1.2069 A, r₀(C–C) = 1.4584 A, r₀(C–H) = 1.117 A, ≰HCC = 110° 46′, r₀(C–D) = 1.114 A, and ≰DCC = 110° 30′. The quadrupole coupling constant eqQ was determined as —79.6 Mc/sec for Cl³⁵ and —62.6 Mc/sec for Cl³⁷. For CH₃CCCl³⁵, CH₃CCCl³⁷, CD₃CCCl³⁵, and CD₃CCCl³⁷ experimental values of D_JK and H_JKK were determined from the K structure. To fit the observed fine structure it was necessary to include the third‐order term H_JKK in the expression for the rotational energy.