Intermolecular potentials and rovibrational energy levels of the Ar complexes with HCN and HCCH

Intermolecular interaction potentials for the Ar–C2H2, Kr–C2H2, and Xe–C2H2 weakly bound complexes: Information from molecular beam scattering, pressure broadening coefficients, and rovibrational spectroscopy

Integral cross sections and pressure broadening coefficients have been measured for the acetylene-krypton complex, by molecular beam scattering and by high resolution IR spectroscopy, respectively. A new potential energy surface (PES) is proposed to describe structure and dynamical properties of this prototypical weakly bound complex. The PES has been parametrized exploiting a novel atom-bond pairwise additive scheme and has been fitted to the experimental data. A similar PES has been obtained for the acetylene-xenon system by a proper scaling of the interaction parameters of the krypton case, based on empirical considerations. These PESs together with that recently proposed by the same authors [J. Phys. Chem. 109, 8471 (2005)] for the acetylene-argon case have been employed for close coupling calculations of the pressure broadening cross sections and for a characterization of the rovibrational structure of the complexes.

Collision Cross Sections, Pressure-Broadening Coefficients and Second Virial Coefficients for the Acetylene-Argon Complex: Experiments and Calculations on a New Potential Energy Surface

Integral cross sections and pressure-broadening coefficients have been measured by molecular beam scattering and by high-resolution infrared spectroscopy, respectively, for the acetylene-argon system. A new potential energy surface (PES) is proposed to describe structure and dynamical properties of this prototypical weakly bound complex. The PES has been parametrized exploiting a novel atom-bond pairwise additive scheme and has been fitted to the experimental data. Calculations of the scattering cross sections (both differential and integral), pressure-broadening, and second virial coefficients have been performed using both the present and also the most recent ab initio PES available in the literature. Analysis of the new experimental data indicates that the anisotropy of the interaction in the well region should be larger than that obtained in ab initio calculations. This is also in line with previous spectroscopic results.

The weakly bound He–HCCCN complex: High-resolution microwave spectra and intermolecular potential-energy surface

Rotational spectra of the weakly bound He-HCCCN and He-DCCCN van der Waals complexes were observed using a pulsed-nozzle Fourier-transform microwave spectrometer in the 7-26-GHz frequency region. Nuclear quadrupole hyperfine structures due to the 14N and D nuclei (both with nuclear-spin quantum number I = 1) were resolved and assigned. Both strong a and weaker b-type transitions were observed and the assigned transitions were used to fit the parameters of a distortable asymmetric rotor model. The dimers are floppy, near T-shaped complexes. Three intermolecular potential-energy surfaces were calculated using the coupled-cluster method with single and double excitations and noniterative inclusion of triple excitations. Bound-state rotational energy levels supported by these surfaces were determined. The quality of the potential-energy surfaces was assessed by comparing the experimental and calculated transition frequencies and also the corresponding spectroscopic parameters. Simple scaling of the surfaces improved both the transition frequencies and spectroscopic constants. Five other recently reported surfaces [O. Akin-Ojo, R. Bukowski, and K. Szalewicz, J. Chem. Phys. 119, 8379 (2003)], calculated using a variety of methods, and their agreement with spectroscopic properties of He-HCCCN are discussed.

Accurate intermolecular ground-state potential-energy surfaces of the HCCH–He, Ne, and Ar van der Waals complexes

Accurate ground-state intermolecular potential-energy surfaces are obtained for the HCCH-He, Ne, and Ar van der Waals complexes. The interaction energies are calculated at the coupled cluster singles and doubles including connected triple excitations level and fitted to analytic functions. For the three complexes we start with systematic basis set studies carried out at several intermolecular geometries, and using augmented correlation consistent polarized valence basis sets x-aug-cc-pVXZ (x=-,d; X=D,T,Q,5), also extended with a set of 3s3p2d1f1g midbond functions. The aug-cc-pVQZ-33211 surfaces of HCCH-He, Ne, and Ar complexes are characterized by absolute minima of -24.22, -50.20, and -122.17 cm(-1) at distances R between the rare-gas atom and the HCCH centers of mass of 4.35, 3.95, and 3.99 A, respectively; and at angles between the vector R and the HCCH main symmetry axis of 0 degrees , 43.3 degrees , and 60.6 degrees . The results are compared and considerably improve those previously available.

Isotopic Study of Rotational Spectra of the Ar-Acetylene Complex

Rotational spectra of the weakly bound complex Ar-acetylene were measured using a Fourier transform microwave spectrometer. Eight additional transitions of the normal isotopomer were detected, following the earlier radiofrequency and microwave investigations [R. L. DeLeon and J. S. Muenter, J. Chem. Phys. 72, 6020-6023 (1980); Y. Ohshima, M. Iida, and Y. Endo, Chem. Phys. Lett. 161, 202-206 (1989)]. Spectra of four minor isotopomers, namely Ar-DCCD, Ar-H(13)C(13)CH, Ar-DCCH, and Ar-H(13)C(12)CH, were newly assigned and analyzed. A semirigid rotor model was employed to obtain the rotational and centrifugal distortion constants, which were in turn used to extract structural information about the complex. The unusually large standard deviations of the spectroscopic fits are indicators of large-amplitude internal motions of the acetylene subunit. Separate fits of the individual K-stacks yielded lower standard deviations, and their results were used to interpret some of the unusual spectroscopic observations. Copyright 2001 Academic Press.

Fourier-Transform Microwave Spectroscopy of the Argon-Diacetylene van der Waals Complex

The rotational spectrum of the argon-diacetylene van der Waals complex, produced in a supersonic molecular beam at 1 K, has been observed with a Fourier-transform microwave spectrometer. We observed 22 a-type rotational transitions with Ka up to 3. Three rotational constants, five centrifugal distortion constants, and one higher-order centrifugal distortion constant were determined precisely by least-squares analysis. The complex is shown to have a planer T-shaped structure with C2v symmetry. The structural analysis provides that the Ar atom is located 3.68 A from the center of mass of diacetylene. Force constants for the van der Waals vibrations were determined from the centrifugal distortion constants. It has been found that this complex has a much steeper and more harmonic intermolecular potential than the argon-acetylene complex. Copyright 1997 Academic Press. Copyright 1997Academic Press