Ab initio calculations of the intermolecular potential energy surface (PES) of CO-N have been carried out using the closed-shell single- and double-excitation coupled cluster approach with a non-iterative perturbative treatment of triple excitations method and the augmented correlation-consistent quadruple-zeta (aug-cc-pVQZ) basis set supplemented with midbond functions. The global minimum (D = 117.35 cm) of the four-dimensional PES corresponds to an approximately T-shaped structure with the N subunit forming the leg and CO the top. The bound rovibrational levels of the CO-N complex were calculated for total angular momenta J = 0-8 on this intermolecular potential surface. The calculated dissociation energies D are 75.60 and 76.79 cm for the ortho-N (A-symmetry) and para-N (B-symmetry) nuclear spin modifications of CO-N, respectively. Guided by these bound state calculations, a new millimeter-wave survey for the CO-N complex in the frequency range of 110-145 GHz was performed using the intracavity OROTRON jet spectrometer. Transitions not previously observed were detected and assigned to the subbands connecting the K = 0 and 1, (j, j ) = (1, 0) states with a new K = 1, (j, j ) = (2, 0) state. Finally, the measured rotational energy levels of the CO-N complex were compared to the theoretical bound state results, thus providing a critical test of the quality of the PES presented. The computed rovibrational wave functions were analyzed to characterize the nature of the different bound states observed for the two nuclear spin species of CO-N.

The rotational spectrum of the van der Waals complex NH 3 -CO has been measured with the intracavity OROTRON jet spectrometer in the frequency range of 112-139 GHz. Newly observed and assigned transitions belong to the K = 0-0, K = 1-1, K = 1-0, and K = 2-1 subbands correlating with the rotationless ( j k ) NH3 = 0 0 ground state of free ortho-NH 3 and the K = 0-1 and K = 2-1 subbands correlating with the ( j k ) NH3 = 1 1 ground state of free para-NH 3 . The (approximate) quantum number K is the projection of the total angular momentum J on the intermolecular axis. Some of these transitions are continuations to higher J values of transition series observed previously [C. Xia et al., Mol. Phys. 99, 643 (2001)], the other transitions constitute newly detected subbands. The new data were analyzed together with the known millimeter-wave and microwave transitions in order to determine the molecular parameters of the ortho-NH 3 -CO and para-NH 3 -CO complexes. Accompanying ab initio calculations of the intermolecular potential energy surface (PES) of NH 3 -CO has been carried out at the explicitly correlated coupled cluster level of theory with single, double, and perturbative triple excitations and an augmented correlation-consistent triple zeta basis set. The global minimum of the five-dimensional PES corresponds to an approximately T-shaped structure with the N atom closest to the CO subunit and binding energy D e = 359.21 cm −1 . The bound rovibrational levels of the NH 3 -CO complex were calculated for total angular momentum J = 0-6 on this intermolecular potential surface and compared with the experimental results. The calculated dissociation energies D 0 are 210.43 and 218.66 cm −1 for ortho-NH 3 -CO and para-NH 3 -CO, respectively. C 2015 AIP Publishing LLC. [http://dx

We report the first high resolution spectroscopic study of the NH 3 -H 2 van der Waals molecular complex. Three different experimental techniques, a molecular beam Fourier transform microwave spectrometer, a millimeter-wave intracavity jet OROTRON spectrometer, and a submillimeter-wave jet spectrometer with multipass cell, were used to detect pure rotational transitions of NH 3 -H 2 in the wide frequency range from 39 to 230 GHz. Two nuclear spin species, (o)-NH 3 -(o)-H 2 and (p)-NH 3 -(o)-H 2 , have been assigned as carriers of the observed lines on the basis of accompanying rovibrational calculations performed using the ab initio intermolecular potential energy surface (PES) of Maret et al. The experimental spectra were compared with the theoretical bound state results, thus providing a critical test of the quality of the NH 3 -H 2 PES, which is a key issue for reliable computations of the collisional excitation and de-excitation of ammonia in the dense interstellar medium.

The rotational spectrum of the van der Waals complex CH 4 -CO has been measured with the intracavity OROTRON jet spectrometer in the frequency range of 110-145 GHz. Newly observed and assigned transitions belong to the K = 2-1 subband correlating with the rotationless j CH4 = 0 ground state and the K = 2-1 and K = 0-1 subbands correlating with the j CH4 = 2 excited state of free methane. The (approximate) quantum number K is the projection of the total angular momentum J on the intermolecular axis. The new data were analyzed together with the known millimeter-wave and microwave transitions in order to determine the molecular parameters of the CH 4 -CO complex. Accompanying ab initio calculations of the intermolecular potential energy surface (PES) of CH 4 -CO have been carried out at the explicitly correlated coupled cluster level of theory with single, double, and perturbative triple excitations [CCSD(T)-F12a] and an augmented correlation-consistent triple zeta (aVTZ) basis set. The global minimum of the five-dimensional PES corresponds to an approximately T-shaped structure with the CH 4 face closest to the CO subunit and binding energy D e = 177.82 cm −1 . The bound rovibrational levels of the CH 4 -CO complex were calculated for total angular momentum J = 0-6 on this intermolecular potential surface and compared with the experimental results. The calculated dissociation energies D 0 are 91.32, 94.46, and 104.21 cm −1 for A ( j CH4 = 0), F ( j CH4 = 1), and E ( j CH4 = 2) nuclear spin modifications of CH 4 -CO, respectively. C 2015 AIP Publishing LLC. [http://dx

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