Millimeter-wave spectroscopy and coupled cluster calculations for NCCP

Abstract

The rotational spectrum of the unstable NCCP molecule has been investigated in the millimeter-wave region. The ground-state spectra of the most abundant isotopomer and of the C-13 and N-15 containing species were studied, and lines in the upsilon(2), upsilon(3), upsilon(4), and upsilon(5) vibrationally excited states were detected for the normal isotopomer. Electric quadrupole and magnetic spin-rotation coupling constants of the nitrogen nucleus were also determined. The experimental work was assisted by high level coupled-cluster single double triple [CCSD(T)] calculations, performed using the cc-pVQZ basis, which provided accurate predictions for the alpha(r) vibration-rotation coupling constants and the ground-state rotational constants of the less abundant isotopic species. r(0) and r(s) molecular structures of NCCP were derived directly from the experimental ground-state rotational constants of four different isotopomers, and an accurate equilibrium structure could be evaluated by combining theoretically computed vibration-rotation coupling constants with experimental ground-state rotational constants. (C) 2000 American Institute of Physics. [S0021-9606(00)00928-4].