The vibrational spectra of some isotopic species of propionitrile

The infrared and Raman spectra of CH₃CH₂CN, CH₃CD₂CN, and CD₃CH₂CN, and the infrared spectrum of CH₃CH₂¹³CN were investigated in detail between 6000 and 100 cm⁻¹. Some infrared measurements of other isotopic species are also reported and partial assignments given. All fundamentals of propionitrile-d₀, -d₂, -d₃, and -¹³CN were assigned, together with a large number of mainly binary combination bands for which a general method of assignment is given. Several Fermi resonances were detected and the unperturbed positions of some of the levels involved were calculated. Special attention was paid to the CH stretching vibrations for which persisting wrong assignments exist in the literature, and to the methyl torsion frequencies which were determined for the four isotopic species above. A valence force field was calculated, and the potential energy distribution of the normal vibrations is tabulated.     

Force field calculations of acetonitrile using CNDO/force method

The redundancy-free internal valence force field (RFIVFF) of acetonitrile is reported using CNDO/force method. The initial force field is set up by taking the interaction and bending force constants from CNDO force field and transferring stretching force constants from the force fields of chemically related molecules. The final force field is obtained by refining the initial force field using vibrational harmonic frequencies of CH₃CN,¹³CH₃CN, CH₃ ¹³CN, CH₃C¹⁵N, CD₃CN and CD₃ ¹³CN. The final force field thus obtained is found to be excellent on the basis of frequency fit and potential energy distribution.     

Methanol and deuterated species: Infrared data,valence force field,rotamers, and conformation

New infrared measurements of gaseous and matrix-isolated methanol and 7 deuterated species are presented and analyzed. A revised assignment for the species CH₃OH(D) and CD₃OH(D) is used to determine 15 significant parameters of a valence force field by a converged simultaneous least-squares adjustment to 44 observed fundamentals. The respective frequencies calculated for the rotamers of CH₂DOH(D) and CHD₂OH(D) turn out to be a valid prediction as they are used to assign 78 observed fundamentals of the species with partially deuterated methyl groups. The values of the 15 force constant parameters are refined by including all 122 observed fundamentals. The force field contains significant deviations from local C_3v symmetry of the methyl group. Such an asymmetry, in the CH-stretching diagonal part, produces a difference of about 10 cm^?1 in the zero point energy of symmetric and asymmetric rotamers of the species with partially deuterated methyl groups. Calculations based on equilibrium structures with and without methyl tilt yield better agreement with observed data in the nontilted case. A preliminary calculation of relative intensities reproduces the major effects of isotopic substitution and rotational isomerism. Experimental evidence for the staggered conformation is obtained from a comparison of observed data with calculated results based on staggered and eclipsed models.     

Methyl cianide: Spectroscopic studies of isotopically substituted species,and the harmonic potential function

The infrared gas-phase spectra of CH₃CN, ¹³CH₃CN, CH₃¹³CN, CH₃C¹⁵N, CD₃CN, and CD₃¹³CN have been studied in detail, in order to determine accurately the fundamental vibration frequency displacements on heavy isotopic substitution. A number of important Fermi resonances have been identified, and treated quantitatively. The unperturbed fundamental frequencies and heavy isotopic displacements form a self-consistent set of data, which, together with Coriolis zeta and centrifugal distortion constants, enable the harmonic potential function of methyl cyanide to be determined with only one constraint. A comparison between the latter and results from an ab initio calculation reveals disagreement in the values of two interaction constants, which seem well outside our experimental error. Infrared frequencies in crystalline films of CD₃CN and CD₃¹³CN at 78 K are also reported.     

Uniqueness of methyl fluoride force field

The uniqueness of the general harmonic force field of methyl fluoride is analyzed. The analysis is applicable to other methyl halides as well. Through the compliance scheme, it is seen that by supplementing the data employed by Aldous and Mills (i.e., vibrational frequencies ω_i, Coriolis coupling constants ζ_i and the centrifugal stretching constants D_J, D_JK of CH₃F and CD₃F molecules), with the frequencies of A′ or A″ species of either CH₂DF or CD₂HF, the force field is uniquely determined. The addition of any other extra data including the ¹²CH₃F¹³CH₃F isotopic shifts only makes the determination of the force field parameters more precise.     

High resolution Fourier transform infrared spectroscopy on CH2DI and CHD2I: evaluation of the ground state constants and analyses of the C-I stretching bands ν3

Abstract

The high resolution (0.0010cm^?1) Fourier transform infrared spectra of the partially deuterated methyl iodide molecules CH₂DI and CHD₂1 have been recorded and analysed in the ν₃ band regions around 510cm^?1. The fundamental band ν₃ is associated with the stretching of the C-I bond and the spectra appear therefore as an asymmetric rotor hybrid a/b-type band and hybrid a/c-type band for CH₂DI and CHD₂I, respectively. About 4700 transitions in the case of CH₂DI and about 3900 transitions in the case of CHD₂I have been assigned. The ground state rotational constants of CH₂DI and CHD₂I have been obtained using the ground state combination differences calculated from the assigned ν₃ transitions and 16 microwave transitions from literature. The S reduced Watson's Hamiltonian has been used in the calculations. In addition, the upper state parameters describing the v₃=1 vibrational states of these molecules have been determined. The obtained ground state constants as well as the upper state parameters have been compared to the corresponding constants of the symmetric top species CH₃I and CD₃I     

Raman spectra of acetonitrile in imidazolium ionic liquids

Raman spectra of dilute solutions of acetonitrile in ionic liquids reveal the characteristic features of ionic liquids' polarity. This is accomplished by investigating the Raman bandshape of the ν (CN) band, corresponding to the CN stretching mode of CH₃CN, which is a very sensitive probe of the local environment. The amphiphilic nature of the CH₃CN molecule allows us to observe the effect of electron pair acceptor and electron pair donor characteristics on ionic liquids. It has been found that the overall polarity of nine different ionic liquids based on 1‐alkyl‐3‐methylimidazolium cations is more dependent on the anion than cation. The observed wavenumber shift of the ν (CN) band of CH₃CN in ionic liquids containing alkylsulfate anions agrees with the significant different values previously measured for the dielectric constant of these ionic liquids. The conclusions obtained from the analysis of the ν (CN) band were corroborated by the analysis of the symmetric ν₁ (CD₃ ) stretching mode of deuterated acetonitrile in different ionic liquids. Copyright © 2010 John Wiley & Sons, Ltd.     

The adsorption and reaction of Acetonitrile on clean and oxygen covered Ag(110) surfaces

The adsorption and reaction of acetonitrile (CH₃CN) on clean and oxygen covered Ag(110) surfaces has been studied using temperature programmed reaction spectroscopy (TPRS), isotope exchange, chemical displacement reactions and high resolution electron energy loss spectroscopy (EELS). On the clean Ag(110) surface, CH₃CN was reversibly adsorbed, desorbing with an activation energy of 10 kcal mol^-1 at 166 K from a monolayer state and at 158 K from a multilayer state. Vibrational spectra of multilayer, monolayer and sub-monolayer CH₃CN were in excellent agreement with that of gas phase CH₃CN indicating that CH₃CN is only weakly bonded to the clean Ag(110) surface. On the partially oxidized surface CH₃CN reacts with atomic oxygen to form adsorbed CH₂CN, OH and H₂O in addition to forming another molecular adsorption state with a desorption peak at 240 K. This molecular state shows a CN stretching frequency of 1840 cm^-1, which is indicative of substantial rehybridization of the CN bond and is associated with side-on coordination via the π system. The CH₂CN species is stable up to 430 K, where C-H bond breaking and reformation begins, leading to the formation of CH₃CN at 480 K and HCN at 510 K and leaving only carbon on the surface. In the presence of excess oxygen atoms C-H bond breaking and reformation is more facile leading to additional desorption peaks for CH₃CN and H₂O at 420 K. This destabilizing effect of O_(a) on Ch₂CN_(a) is explained in terms of an anionic (CH₂CN^-1) species. Comparison of the vibrational spectra from CH₂CN_(a) and CD₂CN_(a) supports the following assignment for the modes of adsorbed CH₂CN: ν(Ag-C) 215: δ(CCN) 545; ϱ_t(CH₂) 695; ϱ_w(CH₂) 850; ν(C-C) 960; ϱ_r(CH₂) 1060; δ(CH₂) 1375; ν(CN) 2075; and ν(CH₂) 2940 cm^-1. These results serve to further indicate the wide applicability of the acid-base reaction concept for reactions between gas phase Brönsted acids and adsorbed oxygen atoms on solver surfaces.     

Determination of force fields for two conformers of nitromethane bycndo/Force method

cndo/Force method is used to evaluate the redundancy free internal valence force fields for two conformers of nitromethane. The initial force field is set up by taking the interaction and bending force constants from this method and transferring the stretching force constants from the force fields of chemically related molecules. The final force field is obtained by refining the initial force field using vibrational frequencies of isotopic speciesviz CH₃NO₂, CD₃NO₂, CH₃ ¹⁵NO₂ and CH₃N¹⁸O₂. The final force field thus obtained is reasonable on the basis of frequency fit and potential energy distribution. The barrier to internal rotation is found to be 0.048 kcal mol⁻¹.     

Vibration-rotation spectra and molecular force field of methylene fluoride and methylene fluoride-d2

Infrared spectra of CH₂F₂ and CD₂F₂ have been measured under a medium resolution. The vibration-rotation bands of CD₂F₂ fundamentals have been analyzed and the assignment for the fundamentals of CD₂F₂ is given. In addition, a number of overtone and combination bands are observed for CH₂F₂, which helps to clarify the vibrational assignment for CH₂F₂. A normal coordinate treatment has been carried out: The force constants in a modified Urey-Bradley as well as the general valence force fields have been determined, the vibrational frequencies and the centrifugal distortion constants obtained from microwave spectroscopy being used. The force constants of the methylene fluoride molecule are discussed in connection with those of the related molecules. Special features of the CH₂F₂ and CD₂F₂ spectra are also described.     

The vacuum ultraviolet spectra of HCN,C2N2, and CH3CN

Quantitative vacuum ultraviolet absorption spectra for HCN, C₂N₂, and CH₃CN have been obtained over the wavelength range 60 nm ? λ ? 160 nm. Where comparison is possible, our measurements of the absorption coefficients for HCN and C₂N₂ are consistent with previous studies. Because of the superior resolution of this work (0.05 nm), vibrational assignments in the valence and Rydberg transitions of HCN have been extended while higher members of the Rydberg series in CH₃CN have been identified.     

Vibrational spectra of nitromethanes and the effects of internal rotation

Infrared spectra have been obtained in gas and crystalline phases for CH₃NO₂, CD₃NO₂, and CHD₂NO₂. A few Raman liquid measurements have also been made. The crystal spectra show the methyl group to be locked in conformation I,

with isolated CH stretching frequencies 3065 (ν_∥CH) and 3000 (ν_⊥CH), respectively. In the gas phase, the bands due to ν_aCH₃ and ν_aCD₃ are split, the splitting being compatible with isolated frequencies of 3065 (ν_∥CH) and 3006 (ν_⊥CH) cm^?1, respectively. These indicate a variation of 0.006 Å in bond length during internal rotation. The gas phase infrared band at 3028.7 cm^?1 and the Raman liquid band at 3024 cm^?1 in the spectra of CHD₂NO₂ represent averages of the frequencies during internal rotation. All calculations are performed with a potential function involving variations both in diagonal bond stretching, and in off-diagonal stretching interaction constants, proportional to cos2π, where π is the internal rotation angle.In the Appendix, vibrational assignments below 1600 cm^?1 are examined. Product rule considerations and intensity changes upon deuteration lead to a conflict with the infrared gas phase band contour over the assignment of the rCD₃ mode at 884 cm^?1. This and other features in the gas phase spectra may arise from the internal rotation.     

氘代最简单Criegee中间体CD2OO的振转光谱研究

本文采用振动自洽场/虚组态相关(VSCF/VCI)方法计算了氘代最简单Criegee中间体CD₂OO的振动和转动光谱. 计算得到的基频振动频率和转动常数与已有实验吻合. 这些数据可以用于未来该体系的光谱研究,特别是振动激发的转动常数对于实验光谱指认非常重要. 另外,不同来源的光谱强度,包括本文理论计算,文献中在NEVPT2和B3LYP水平上的计算结果以及实验结果,互相之间均不符合.     

Vibrational spectra of (CD3)2Cd and (CD3)2Zn

The Raman and infrared spectra of (CH₃)₂Cd and (CH₃)₂Zn have been reexamined and are reported along with previously unreported vibrational data for (CD₃)₂Cd and (CD₃)₃Zn. The spectra have been analyzed using the double group $\text{G}{}_{36}\text{2}$, which has led to some changes in assignments made previously. Comparison is also made with a recent study of (CH₃)₂Hg and (CD₃)₂Hg. Fine structure was observed for two of the vibrations of the E_1d symmetry species, arising from internal rotation of the methyl groups. This structure has been analyzed using a recently developed theory for molecules of the freely rotating dimethylacetylene type. Problems which arise in the application of this theory have been pointed out, and it is suggested that some additional consideration of the theory may be necessary.     

Discovery and frequency measurement of short-wavelength far-infrared laser emissions from optically pumped <Superscript>13</Superscript>CD<Subscript>3</Subscript>OH and CHD<Subscript>2</Subscript>OH

A three-laser heterodyne system was used to measure the frequencies of twelve previously observed far-infrared laser emissions from the partially deuterated methanol isotopologues ¹³CD₃OH and CHD₂OH. Two laser emissions, a 53.773 μm line from ¹³CD₃OH and a 74.939 μm line from CHD₂OH, have also been discovered and frequency measured. The CO₂ pump laser offset frequency was measured with respect to its center frequency for twenty-four FIR laser emissions from CH₃OH, ¹³CD₃OH and CHD₂OH. PACS 07.57.Hm; 42.55.Lt; 42.62.Eh     

Methylene chloride: The mid-infrared spectrum of an almost vibrationally unperturbed molecule

The infrared gas phase spectra of ¹²CH₂Cl₂, ¹³CH₂Cl₂, and ¹²CD₂Cl₂ have been studied in the region below 6200 cm⁻¹ under conditions of high resolution. Some 30 vibrational levels can be identified for each isotopic species and assigned unequivocally in terms of the band contours displayed. Direct observation has been made of the very weak ν₂ fundamentals in all species, and of the “inactive” torsion fundamental of CD₂Cl₂. Rotational analyses have been performed on the observed Q-branch features of over 30 bands. For each isotopic species, it is found, with one exception, that all vibration levels fit accurately the simple second-order perturbation expression involving ν′s and x′s. The sole exception in each species is the overtone region of the CH₂(CD₂) stretching vibrations. Here anharmonicity effects bring vibrationally interacting levels into close enough proximity for resonance effects to become just slightly more than of second-order importance. Full analyses including Fermi resonance are made. The effects of the Darling-Dennison resonance between the overtones of the CH stretching fundamentals are observed and corrected for in terms of a simple assumption. Most of the resulting anharmonicity constants bear isotopic relationships similar to those established for H₂O and D₂O. It is concluded that, with the exception of the CH(CD) stretching overtone region, methylene chloride isotopomers behave as vibrationally unperturbed molecular systems in the mid-infrared region.     

Atomic and molecular adsorption on Pd(111)

The adsorption properties of a variety of atomic species (H, O, N, S, and C), molecular species (N₂, HCN, CO, NO, and NH₃) and molecular fragments (CN, NH₂, NH, CH₃, CH₂, CH, HNO, NOH, and OH) are calculated on the (111) facet of palladium using periodic self-consistent density functional theory (DFT–GGA) calculations at ¼ ML coverage. For each species, we determine the optimal binding geometry and corresponding binding energy. The vibrational frequencies of these adsorbed species are calculated and are found to be in good agreement with experimental values that have been reported in literature. From the binding energies, we calculate potential energy surfaces for the decomposition of NO, CO, N₂, NH₃, and CH₄ on Pd(111), showing that only the decomposition of NO is thermochemically preferred to its molecular desorption.     

Vibrational assignments and force field calculations for trimethylarsenic dichloride,dibromide and their deuterated analogs

Raman and infrared spectra have been recorded for trimethylarsenic dichloride, dibromide and their deuterated analogs and vibrational assignments were made for the skeletal modes of these compounds. The spectra of the dichloride and its deuterated analog were interpreted in terms of a trigonal bipyramidal structure, D_3h symmetry, whereas the spectra of the dibromides were interpreted using the ionic model, [(CH₃)₃AsBr]⁺Br⁻, having C_3v symmetry. Using a generalized valence force potential field, normal coordinate analyses data were obtained for the dichloride and the dibromide. Included in this data are potential energy distributions for a set of symmetry coordinates. The force fields obtained for the dichloride and dibromide were used to calculate frequencies for the corresponding deuterated compounds. The discrepancies between the observed and calculated frequencies for the deuterated compounds are discussed in terms of the assumptions made.     

Overlapping spectral features and new assignment of 2‐propanol in the C–H stretching region

The vibrational spectra of gaseous and liquid 2‐propanol in the C–H stretching region of 2800 ~ 3100 cm⁻¹ were investigated by polarized photoacoustic Raman spectroscopy and conventional Raman spectroscopy, respectively. Using two deuterated samples, that is, CH₃CDOHCH₃ and CD₃CHOHCD₃, the overlapping spectral features between the CH and CH₃ groups were identified. With the aid of depolarization ratio measurements and density functional theory calculations, a new spectral assignment was presented. In the gas phase, the band at 2884 cm⁻¹ was assigned to the overlapping of one CH₃ Fermi resonance mode and a CH stretching of gauche conformer. The bands at 2917 and 2933 cm⁻¹ were assigned to another two CH₃ Fermi resonance modes, but the latter includes weak contribution from CH stretching of trans conformer. The bands at 2950 and 2983 cm⁻¹ were assigned to CH₃ symmetric and antisymmetric stretching, respectively. The spectral features of liquid 2‐propanol are similar to those in the gas phase except for the blue shift of CH and the red shift of CH₃ band positions, which can be attributed to the intermolecular interaction in the liquid state. The new assignments not only clarify the confusions in previous studies from different spectral methods but also provide the reliable groundwork on spectral application of 2‐propanol in the futures. Copyright © 2014 John Wiley & Sons, Ltd.