The rotational spectrum of propynyl isocyanide

Propynyl isocyanide, CH3C2NC, has been prepared by vacuum pyrolysis of pentacarbonyl-(1,2-dichloropropenyl isocyanide) chromium, (CO)(5)Cr-CN-C(Cl) = C(Cl)CH3, and its ground state millimeter and microwave spectrum has been observed for the first time. I; structural parameters of this molecule with a C-3 nu symmetry could be obtained from the rotational constants of several isotopomers: R(C1-C2) = 1.456(2) Angstrom, r((C2-C3)) = 1.206(2) Angstrom, r((C3-N)) = 1.316(2) Angstrom, r((N-C4)) = 1.175(2) Angstrom, r(H-Cl) = 1.090(1) Angstrom, > HCC = 110.7(4)degrees. The nitrogen quadrupole coupling constant has been determined to be 878(2) kHz and measurements of the Stark effect allowed to obtain an electric dipole moment of 4.19(3) Debye. The results fit well into a series of related compounds and are in good agreement with data from ab initio calculations. (C) 2000 Elsevier Science B.V. All rights reserved.