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A study was conducted relating to research on the vibrational spectrum of ethanol monomers and the issue of the rotational isomerism of ethanol was conducted. The experiment aimed to demonstrate that the comparison between spectra calculated according to the DFT method for both conformers and the observed ones enable researchers to conclude that either one or the other species can be stabilized according to the nature of the matrix. Results of the study are discussed.

The simultaneous existence of valence and dipole-bound states of the uracil anion was investigated in a cross beam experiment. Specifically, Rydberg electron attachment to gas-phase isolated uracil molecules and mixed uracil-argon clusters was analyzed. Field-detachment measurements showed that attachment and evaporation of a single argon atom is enough to switch from dipole-bound to valence monomer uracil anions. The results were consistent with two previous theoretical predictions.

Studies infrared induced isomerization of methanol-acetonitrile mixed aggregates trapped in argon and nitrogen matrices. Use of an optical parametric oscillator for monochromatic irradiations at the OH and CH stretching frequencies of complexed methanol; Characterization of several forms of the 1:1 complex by most of the vibrational modes.

Discusses why density functional theory (DFT) and hybrid Hartree-Fock/DFT techniques fail to predict reliable frequency shifts for the proton donor when anharmonicity is taken into account. Approximate procedure of anharmonic shift calculation; Basis of MP3 results obtained on a series of complexes in which hydrogen fluoride is the proton donor.

The electronic and geometrical structures of the water dimer anion are investigated by density functional calculations. Theoretical values of the very weak electron affinities and vertical detachment energies show good agreement with available experimental data. It is predicted that a significant modification of the neutral parent geometry is introduced by the electron attachment process and leads to a large excitation of anion intermolecular modes. The interpretation of field-detachment experiments of (H2O)-2 and (D2O)-2, produced in collisions between laser-excited Rydberg atoms and cold neutral water clusters, confirms the existence of large amplitude low-frequency motions in the anions. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The LiCO molecule has been previously characterized experimentally in rare gas matrices by a large red shift of the CO stretching mode and a Li–C vibration around 600 cm-1 indicating a relatively strong Li–C bonding. Up to now, post Hartree–Fock ab initio methods had described this complex as unstable in its electronic ground state and predicted a linear metastable structure owing to strong induction forces between this complex and the surrounding polarizable rare gas atoms. Electronic and vibrational calculations at the harmonic approximation on this molecule using approximate density functional theory give results which are better in line with the experimental results. Two distinct bounded structures are found to be stable in the electronic ground state for the LiCO complex. The credibility of these calculations is also assessed in two ways; the first one is the comparison between experimental and calculated vibrational analysis on the νCO modes of the Li(CO)n (n=2,3) complexes. The second one is the study of the eventual complexation of Na and K atoms with the CO molecule and the comparison with experimental available data. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Due to their importance in stratosphere, spectroscopic studies of halogenated carbonyls (COF2, COFCl, COCl2) and their complexes with Cl2 are reviewed, including previously unpublished data. In particular, quantitative analysis of νCO Fermi resonance has been made for free and complexed halogenated carbonyls. Ab initio calculations have been undertaken on all these structures. The structure, complexation energy and vibrational analysis at the harmonic approximations have been calculated at the self-consistent field and Mo\ller–Plesset 2 levels. The calculated frequency shifts are in overall agreement with the experimental data. This result was not obvious owing to the weakness of the complexes. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The infrared spectrum of the CH3OH:H2O complex isolated in a nitrogen matrix is here reported. The complex is identified through observation of all three internal modes of the water moiety and 10 out of 12 vibrations of the methanol subunit. Several conformers of the CH3OH...OH2 are evidenced through ir photochemical and thermal conversion process, but none corresponds to the reverse CH3HO...HOH structure, with water playing the role of the proton donor. Ab initio calculations on both structures have been performed to obtain their equilibrium geometries and vibrational spectra. They allow to account for the ir spectral changes (frequencies as well as intensities) of the two submolecules interacting through hydrogen bonding within the complex. [ABSTRACT FROM AUTHOR]

The substructure of the infrared spectrum for acetone-HF hydrogen-bonded complex has been reconstructed for the first time using ab initio calculations at the self-consistent-field approximation. Vibrational calculations of the νFH and νF···O transitions taking into account the mechanical anharmonicity effects have been made using a variational method. The main shoulders of the infrared spectrum are interpreted in terms of combination transitions and hot combination transitions. [ABSTRACT FROM AUTHOR]

The FH···NCH hydrogen-bonded complex, which is a reference structure, has been reviewed from an electronic and vibrational point of view. Ab initio calculations have been made, using a large basis set and thus providing first structural and electrical properties on the subunits when the electronic correlation effects are taken into account in very close agreement with the experimental data. The structure and dipole moment of the complex are well represented. The νFH and νF···N stretching modes are calculated by means of the variational method, taking into account the mechanical anharmonicity and anharmonic coupling between both vibrations. It is shown that the νF···N stretching frequency, which is larger than the experimental value at the self-consistent-field level and especially when electronic correlation effects are taken into account, is strongly decreased, and so approaches the experimental value, when corrected for basis set superposition error. [ABSTRACT FROM AUTHOR]

This paper presents the first ab initio attempt to construct the stretching fundamentals νFX and νF...N (X=H, D, Li) in the FX...NH3 complexes taking into account the mechanical anharmonicity. A potential-energy surface V(rFX,RF...N) grid was generated at the self-consistent-field and second-order Mo\ller–Plesset levels. The coefficients fitting the potential-energy surface up to the fourth order have been used to compute the νFX and νF...N stretching modes. The vibrational problem is solved by means of a variational treatment which includes the effects of mechanical anharmonicity. The results are compared with the available experimental data. [ABSTRACT FROM AUTHOR]

This paper presents the first ab initio attempt to reconstruct the observed band profile of the stretching fundamental vFX (X=H,D) in the FX···O(CH3)2 hydrogen-bonded system. The two-dimensional potential energy surface V(rFH,RF···O) is evaluated by means of large basis set SCF calculations. The related force constants up to the fourth order are obtained via the analytical fit to a polynomial expansion. The vibrational problem is solved by means of a variational treatment which includes the effects of mechanical anharmonicity. The side bands of the stretching fundamental vFX are described in terms of the vFX ±nvFX···O combination bands in excellent agreement with experiment. [ABSTRACT FROM AUTHOR]

Calculates the electronic affinity and vertical detachment energy of the water dimer complex using the density functional theory. Location of the excess electron; Inability of the conventional post Hartree-Fock correlation schemes to predict water dimer electronic affinity; Analysis of spin density.

Quantum chemical calculations on the Li–C2H4 complex have been performed with coupled-cluster and density functional methods. For both methods the electronic ground state of the complex is calculated to be 2B2, with a C2v symmetry equilibrium structure, and the calculated binding energy is quite small (around 2 kcal/mol), and therefore very much basis set dependent. The vibrational spectrum has been calculated at the harmonic approximation, including 13C/12C, 7Li/6Li, and H/D isotopic substitutions. The agreement between experimental and calculated infrared frequencies is correct, except for the low frequency symmetric Li–C stretching mode. These calculations also allow to propose an assignment for the observed C–H/C–D stretching modes. The observed blue-shift of the symmetric CH2 bending mode as well as the red-shift of the antisymmetric CH2 bending, CD2 bending, and C–C stretching modes with respect to the free ethylene have been confirmed by the density functional calculations. The Na...C2H4 complex has been found to be unstable in its 2B2 electronic state. The study of the 2A1 electronic state for both Na...C2H4 and K...C2H4 complexes show that they are at most very weak van der Waals complexes. This result confirms the conclusions of matrix isolation experiments. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Ab initio self-consistent field (SCF) and MP2 calculations have been performed in order to investigate the structure, energetics, and spectroscopic properties of H2O: (HF)2. Two conformations of the 1:2 complex are energetically possible. On the one hand is a cyclic complex belonging to the C1 point group and which corresponds to the absolute minimum, and on the other hand is a bifurcated complex with C2v symmetry. In this latter complex the two hydrogen bonds are equivalent whereas in the former there are two strong H-bonds and a weaker one. The energy difference between these two conformers is ∼3 kcal mol-1. From the spectroscopical point of view the bifurcated complex is characterized by νHF frequency shifts smaller than that calculated for the dimer, in the case of the cyclic complex the two different νHF red shifts closely related to the H2O–HF and (HF)2 calculated shifts, respectively, and correspond to those experimentally observed. The cooperative effects on interaction energies and spectroscopic properties have been estimated and analyzed on the basis of the projected induced dipole moment. It is shown that the cyclic complex is favored with respect to both H2O–HF and (HF)2 precursors while the formation of the bifurcated one remains more problematic. [ABSTRACT FROM AUTHOR]

A series of self-consistent field (SCF) calculations has been carried out on the 1:1 hydrogen bonded complexes of water and hydrogen halide (HF,HCl,HBr,HI) using core pseudopotentials and PS-31G** basis sets. The geometry optimization confirm the Cs structure predicted by the Legon–Millen rules. Electron density difference (complex superposition of isolated molecules) emphasize the role of polarization effects in this type of hydrogen bond. Finally, the HX frequency shifts with respect to monomeric species, the intensity ratios of the corresponding IR lines and the intermolecular stretching frequencies have been calculated by a variational method which takes into account both coupling and anharmonicity effects. An overall agreement with experimental data is obtained for these spectroscopic properties. [ABSTRACT FROM AUTHOR]