Fermi interaction between the nu1 and the nu2+4nus bands of ArDN2+.

Two rotationally fully resolved vibrational bands have been assigned unambiguously to the linear deuteron bound Ar¯DN2 + complex by using ground state combination differences. The ionic complex is formed in a supersonic planar plasma expansion optimized and controlled by a mass spectrometer and is detected in direct absorption using tunable diode lasers and applying production modulation spectroscopy. The band origins are located at 2436.272 cm-1 and at 2435.932 cm-1 and correspond to the 1 band NN stretch and to the 2+4s combination band DN and intermolecular stretch, respectively. The two bands overlap strongly and the large intensity of the combination band is explained in terms of a Fermi interaction. This interaction perturbs the observed transitions, particularly for low J values. Least-squares fitting yields values for the Fermi interaction parameters of F0=0.332 cm-1 and FJ=-0.001 46 cm-1 and results in accurate rotational constants. These are discussed both from an experimental and a theoretical point of view.