Analysis of the rotational spectrum of pyruvonitrile up to 324 GHz

The room-temperature rotational spectrum of pyruvonitrile (acetyl cyanide, CH3COCN) was measured up to 324 GHz, and additional measurements were also made in supersonic expansion in the region 719 GHz. The available data sets for the A and E torsional sublevels were extended to over 1200 transitions, J = 65 and K, = 38 for the ground vibrational state, and to comparable numbers of transitions for first excited states of the methyl torsional mode v(18), and the in-plane CCN bending mode v(12). The collected experimental measurements were fitted with several different computer programs for dealing with the effects of methyl torsional motion on the rotational spectrum and many spectroscopic constants have been determined. The experimental results are discussed in detail and are augmented by ab initio computations. Stark effect measurements in supersonic expansion were used to precisely determine the electric dipole moment of pyruvonitrile, vertical bar mu(a)vertical bar = 2.462(2) D, vertical bar mu(b)vertical bar = 2.442(2) D, mu(tot) = 3.468(2) D. Pyruvonitrile, as an 8-atom molecule with a sizable dipole moment, is a possible candidate for astrophysical detection and the present Work provides the laboratory data necessary for that purpose. (C) 2009 Elsevier Inc. All rights reserved.