BOUND STATE CALCULATIONS OF THE VAN DER WAALS NH3−Ne COMPLEX AND FIRST MICROWAVE DETECTION OF THE MISSING (para)-NH3−Ne NUCLEAR SPIN ISOMER

The microwave spectrum of the NH3−Ne van der Waals complex has been observed in a supersonic molecular jet expansion via broadband (2-8 GHz) chirped-pulse Fourier-transform microwave spectroscopy. Together with the wellknown lines related to the (ortho)-NH3−Ne spectrumb, new transitions were detected and attributed to the missing (para)NH3−Ne nuclear spin isomer. The assignments were guided by the rovibrational bound state (J = 0 ... 10) calculations based on the recent ab initio NH3−Ne intermolecular potential surfacec. The hyperfine structure arising from quadrupole N nucleus of NH3−Ne was resolved, and the quadrupole coupling constant associated with the (para)-NH3 subunit was precisely determined. This constant provided the dynamical information about the angular orientation of ammonia indicating that the average angle between the C3 axis of NH3 and intermolecular axis is about 68◦. Similar results for the deuterated isotopologue, ND3−Ne, were also obtained thus confirming and extending the analysis for the parent NH3−Ne complex.