The Ar–C2H2 intermolecular potential from high resolution spectroscopy and ab initio theory: A case for multicenter interactions

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.

Infrared Optothermal Spectroscopy of N(2)- and OC-DCCH: The C-H Stretching Region

High-resolution optothermal laser spectroscopy is reported for the C-H stretching vibrations of the binary complexes formed between monodeuterated acetylene and carbon monoxide and nitrogen. In contrast with a previous study of the corresponding C(2)H(2) complexes, where the C-H fundamental spectra were highly perturbed [R. D. Beck, A. G. Maki, S.-H. Tseng, and R. O. Watts, J. Mol. Spectrosc. 158, 306-317 (1993)], the present spectra are well described by a simple linear-rotor Hamiltonian. This is presumed to result from the fact that the C-H vibration in the monodeuterated complexes is decoupled from the intermolecular degrees of freedom. Copyright 2000 Academic Press.

HIGH RESOLUTION SPECTROSCOPY IN THE GAS PHASE: Even Large Molecules Have Well-Defined Shapes

▪ Abstract  A review of recent high-resolution microwave, infrared, and optical spectroscopy experiments demonstrates that remarkable progress has been made in the past 20 years in determining the equilibrium geometries of large polyatomic molecules and their clusters in the gas phase, and how these geometries change when the photon is absorbed. A special focus is on the dynamical information that can be obtained from such studies, particularly of electronically excited states.

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