Pulsed molecular beam infrared absorption spectroscopy of the N2CO complex

A rotationally resolved spectrum of the N2CO complex was observed in the region of the CO monomer vibration by a rapid-scan infrared diode laser and a pulsed molecular beam. The Q- and R-branches of the b-type transitions (Ka = 1 ← 0) for N2CO were observed, but the P-branch transition was missing. A fit of the rotational energies to a power series in J(J + 1) showed that the effective centrifugal distortion constants for the ground and excited vibrational states were extraordinarily large. The wavenumber shift from the fundamental line of the CO monomer was much smaller than those for other van der Waals molecules except for molecules with rare gas atoms. These observations suggest that this complex has a weak van der Waals bond and a low barrier to intermolecular rotation.