Millimeter-wave spectra of HCCCN

The rotational spectra of cyanoacetylene (HCCCN) were investigated between 148 and 474 GHz. The assignments were obtained on the basis of a global ana lysis, which uses both vibrational and rotational data available for this m olecule. The 876 new experimental frequencies concern 181 vibrational state s (up to about 1750 cm(-1)). The global analysis agreement is perfect for s tates up to 1300 cm(-1) and the fit remains good for higher energy states. High order anharmonic interactions associated with the k(45577) and k(45666 ) terms of the potential energy, which are not introduced in our model, are responsible for local effects in a few states. The reduced frequencies are plotted for most reported states to illustrate the effects of the numerous interactions. (C) state-by-state fit is also given, but the classical powe r series in J(J + 1) is not convenient for the heavily perturbed states. (C ) 2000 Elsevier Science B.V. All rights reserved.