B.J. van der Veken

An infrared study of monomeric and oligomeric (n=2, 3, and 4) hydrogen chloride in liquified noble gases

Infrared spectra (3100–2600 cm−1) of HCl dissolved in liquid argon (94–124 K), liquid krypton (117–167 K), and liquid xenon (161–221 K) at concentrations varying from 0.8×10−3 to 2.8×10−2 M are reported. At low concentrations in all three solvents, only the spectrum due to monomeric species is observed. For solutions in liquid argon, the observed rotational fine structure was assigned. For all solvents, the monomeric stretching frequency shows a linear relation to the relative density of the solvent, extrapolating to the dilute vapor phase frequency. At higher concentrations in liquid argon and liquid krypton, bands due to oligomeric species are found. Factor analysis shows at least three oligomeric species are present. The band profile analysis of the oligomer absorptions allows the assignment of observed bands to dimer, trimer, and tetramer. From the temperature dependence of the oligomer band intensities, the enthalpy difference for dimerization is found to be 3.78±0.33 kJ mol−1 in liquid argon and 5.0...

Vibrational analysis of arsenic acid and its anions: I. Description of the Raman spectra

Abstract The Raman spectra of arsenic acid and its anions have been recorded. For some regions in the spectra, where overlapping bands arise, a band profile analysis has been performed using the damped least square procedure. The vibrational assignments for the observed frequencies have been proposed and discussed.

On the ethene/HCl Van der Waals complexes observed in liquefied argon and liquefied nitrogen

The mid-infrared (4000–400 cm−1) and far-infrared (300–10 cm−1) spectra of C2H4/HCl mixtures, dissolved in liquefied argon (93–125 K) and in liquefied nitrogen (80–118 K) are discussed. In all spectra, experimental evidence was found for the existence of 1:1 and 1:2 Van der Waals complexes. Using spectra recorded at different temperatures, the complexation enthalpy ΔH° for the 1:1 complex was determined to be −8.7(2) kJ mol−1 in liquid argon and −6.4(4) kJ mol−1 in liquid nitrogen, while for the 1:2 complex a ΔH° of −18.3(6) kJ mol−1 was found. For all species studied, the vibrational frequencies were obtained from ab initio calculations at the MP2/6−311+G** level. Using the SCRF/SCIPCM scheme to correct for the solvent influences, and using statistical thermodynamics to account for the zero-point vibrational and thermal contributions, approximate values for the dissociation energy were calculated from the complexation enthalpies. The resulting values, −12.7(5) kJ mol−1 for the 1:1 complex and −26.9(2) kJ...

Methyl vinyl ketone in the gas phase, investigated by electron diffraction, infrared band contour analysis and microwave spectroscopy, supplemented with ab-initio calculations of geometries and force fields

Abstract The structure of methyl vinyl ketone was studied by the analysis of gas phase electron diffraction, microwave and infrared (IR) data, including band profiles. The experimental data are supplemented with vibrational constraints taken from force-field calculations at the 4-21G ab-initio level and with geometrical constraints arising from molecular mechanics (MMP 1 force field), and geometry relaxed 4-21G and 4-21G** ab-initio calculations. An independent vibrational analysis was performed leading to an assignment of the IR frequencies. A contour analysis allowed unequivocal identification of the ν(CO) band centres and shapes of the two conformers. All data are in accord with the gas phase consisting of ap and sp conformers, at room temperature in the ratio ap : sp = 80 : 20. An enthalpy difference of ΔH = 1.07(10) kcal mol−1 was obtained. A rationalization of why microwave spectroscopy failed to detect the sp conformer was found in the direction and magnitude of its dipole moment as well as in the value of its partition function. The experimental data favour the ab-initio constrained geometrical model, the MMP1 based model could be rejected on statistical grounds. Furthermore, the data are in accord with planar heavy atom skeletons for both the ap and sp forms. Subject to the ab-initio constraints, the internal coordinates (rg distances, r0α angles) were refined to: CO 1.219 A; CC 1.336 A; C(sp2)C(sp2) 1.494 A; C(sp2)C(sp3) 1.520 A; 〈C(sp2)H〉 1.089 A; 〈C(sp3)H〉 1.109 A; CCC(ap) 125.0°; CCC(sp) 120.6°; C(sp2)C(O)C(sp3)(ap) 118.9°; C(sp2)C(O)C(sp3)(sp) 116.1°.

Solvent effect on vibrational frequencies: cryosolution experiments and density functional calculations

Abstract FTIR spectra of C 2 H 6 , COF 2 and CH 3 F in the vapour phase and in solutions in liquefied argon, krypton and xenon were investigated. Vapour–solvent frequency shifts (SFS) were determined for all IR-active fundamentals of the studied compounds. In parallel, the SFS values were calculated using the Self-Consistent Isodensity Polarizable Continuum Model (SCIPCM) at the B3LYP/6-311++G(d,p) level. Comparison of the experimental and the calculated data shows reasonable agreement only for three most intense IR bands under investigation, i.e., the CO and the CF 2 asymmetric stretching modes of COF 2 , and the C–F stretching mode of CH 3 F. For the other bands of COF 2 , CH 3 F and for all the bands of C 2 H 6 the results of SCIPCM calculations underestimate the observed SFS significantly. It is concluded that at least for the modes with relatively small (∂μ/∂Q) o values, the electrostatic interactions give a minor contribution to SFS.

Vibrational spectra, conformational stability, barriers to internal rotation, r0 structural parameters and ab initio calculations of fluoromethyl methyl ether

The far-infrared spectrum of gaseous fluoromethyl methyl ether, FCH2OCH3, along with three of the deuterium isotopes, has been recorded at a resolution of 0.10 cm−1 in the 350 to 50 cm−1 region. The fundamental asymmetric torsional and methyl torsional modes are extensively mixed and have been observed at 182 and 132 cm−1, respectively, for the stablegauche conformer with the lower frequency band having several excited states falling to lower frequency. An estimate is given for the potential function governing the asymmetric rotation. On the basis of a one-dimensional model the barrier to internal rotation of the methyl moiety is determined to be 527±9 cm−1 (1.51±0.03 kcal/mol). A complete assignment of the vibrational fundamentals for all four isotopic species observed from the infrared (3500 to 50 cm−1) spectra of the gas and solid and from the Raman (3200 to 10 cm−1) spectra of the gas, liquid, and solid is proposed. No evidence could be found in any of the spectra for the high-energytrans conformer. All of these data are compared to the corresponding quantities obtained from ab initio Hartree-Fock gradient calculations employing the 3-21G and 6-31G* basis sets along with the 6-31G* basis set with electron correlation at the MP2 level. Additionally, completer0 geometries have been determined from the previously reported microwave data and carbon-hydrogen distances determined from infrared studies. The heavy-atom structural parameters (distances in Å, angles in degrees) arer(C1-F) = 1.395 ± 0.005;r(C1-O) = 1.368 ± 0.007;r(C2-O) = 1.426 ±0.003; ⦔FC1O = 111.33 ± 0.25; ⦔C1OC2 = 113.50 ± 0.18 and dih FC1OC2 = 69.12 ± 0.26. All of these results are discussed and compared with the corresponding quantities obtained for some similar molecules.

Vibrational analysis of methylphosphonic acid and its anions: I. Vibrational spectra

Abstract The vibrational spectra of aqueous solutions of methylphosphonic acid and its anions are reported. Some points of uncertainty in former studies on the dibasic anion are discussed, while the spectra of the acid and monobasic anion are interpreted with the aid of assignments given for the dibasic anion. The effects observed on dilution are discussed.

Vibrational analysis of the oxaniides—the characteristic pattern of amides in i.r. and Raman spectra

Abstract The i.r. and Raman spectra of the oxamides R 1 R 2 NCOCONR 3 R 4 (where R = CH 3 , H or D), have been recorded and the fundamental vibrational frequencies have been assigned; the spectra have been compared with those of other simple amides and we have been able to describe a pattern, characteristic for the amides, in infrared and Raman; these results could be useful in qualitative analysis.

Vibration-rotation spectra of HCl in rare-gas liquid mixtures: Molecular dynamics simulations of Q-branch absorption

New experimental results are presented on the fundamental IR band shape of HCl dissolved in neat liquid Ar and Ar doped with Kr and Xe. A strong enhancement of the absorption in the range of a central Q-branch is observed in the spectra of doped solutions. Semiclassical molecular dynamics simulations of the spectral band profile are carried out using (12-6) Lennard-Jones site–site interaction potentials. The parameters of these model potentials were deduced by fitting the available anisotropic interaction surfaces, accurately describing the structure of binary rare-gas-HCl van der Waals complexes. Simulations realistically reproduce the observed triplet band structure and its evolution with changing thermodynamic conditions. The analysis of the influence of anisotropic interactions on the orientational dynamics of solutes and orientation-dependent radial distribution functions reveals the mechanisms that contribute to appearance of the Q-branches. It is shown that long-living solute-solvent spatial correl...

Conformational analysis and structural determinations from ab initio calculations for chloroacetaldehyde

Abstract Structural parameters for both the more stable s-cis (chlorine atom s-cis to the aldehyde hydrogen atom) and high energy s-trans conformers of chloroacetaldehyde, ClCH 2 CHO, have been obtained from ab initio Hartree-Fock gradient calculations employing the 3-21G ∗ and 6-31G ∗ basis sets with electron correlation. The results are compared to the r a values obtained for the s-cis rotamer from an electron diffraction study as well as with some r o values determined from some previously reported rotational constants for both the s-cis and s-trans conformers. Potential surface calculations have been carried out to determine the barrier to internal rotation and the conformational stability. At the 6-31G ∗ basis set level the s-cis to s-trans barrier is 1203 cm −1 (3.44 kcal mol −1 ) with the s-cis conformer being more stable by 509 cm −1 (1.46 kcal mol −1 ) than the s-trans form. There is a small “hump” of 12 cm −1 (34 cal mol −1 ) at the s-cis position which is below the first torsional energy level for this conformer. Infrared band contour simulation of the carbon-chlorine stretching mode for fluoroacetyl chloride predicts an s-trans to gauche equilibrium which is inconsistent with the ab initio results where the high energy conformer is predicted to have the s-cis structure. All of these results are compared with the corresponding data for some similar molecules.