Fermi Resonance Interaction Research Articles

Renner-Teller, spin-orbit and Fermi-resonance interactions in X 2Π NCS investigated by LIF spectroscopy

The electronic spectrum of the NCS radical is obtained following UV excimer-laser photolysis of C2H5NCS in a large excess of inert gas in a supersonic free jet expansion. The spectrum is complicated by the presence of Renner-Teller and spin-orbit coupling and a Fermi resonance between the doubly excited bending vibration and v 3, the CS stretching vibration. Bending vibronic level structure in the X 2Π ground state of the radical is determined from a variety of laser-induced-fluorescence techniques, including stimulated-emission pumping. These energy levels are used to determine vibronic-coupling parameters for the radical. Coupling between close-lying bending levels with different v 2 and K (= Λ + l) is found to be important because some of these levels are close together in NCS owing to the very large spin-orbit coupling. A parameter representing this effect is related to the dipolar contribution ε1 to the Renner-Teller coupling parameter ε by applying perturbation theory to a simple model involving the X 2Π and B 2Σ+ electronic states of NCS. This procedure results in an estimate for ε1 that agrees approximately with that determined from the vibronic-coupling parameter g K, assuming the same model for the interacting electronic states.

Solvent-Induced Nitrile Frequency Shifts: Acetonitrile and Benzonitrile

The C≡N stretching frequency, vC≡N, is affected by change in the solvent and also by change in concentration in the same solvent. In the case of acetonitrile, vC≡N is in Fermi resonance with the combination tone (δsym. CH3 + vC-C), and the degree of Fermi resonance interaction changes with change in the solvent. With the exception of dimethyl sulfoxide, unperturbed vC≡N for acetonitrile exhibits a pseudo-linear correlation with the acceptor number of the solvent.

ChemInform Abstract: Vibrational Anharmonicity, Fermi Resonance Interactions, and Local Mode Behavior in CH3Cl.

ChemInformVolume 21, Issue 27 Physical Organic Chemistry ChemInform Abstract: Vibrational Anharmonicity, Fermi Resonance Interactions, and Local Mode Behavior in CH3Cl. J. L. DUNCAN, J. L. DUNCAN Dep. Chem., Univ. Aberdeen, Meston Walk, Old Aberdeen AB9 2UE, UKSearch for more papers by this authorM. M. LAW, M. M. LAW Dep. Chem., Univ. Aberdeen, Meston Walk, Old Aberdeen AB9 2UE, UKSearch for more papers by this author J. L. DUNCAN, J. L. DUNCAN Dep. Chem., Univ. Aberdeen, Meston Walk, Old Aberdeen AB9 2UE, UKSearch for more papers by this authorM. M. LAW, M. M. LAW Dep. Chem., Univ. Aberdeen, Meston Walk, Old Aberdeen AB9 2UE, UKSearch for more papers by this author First published: July 3, 1990 https://doi.org/10.1002/chin.199027038AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume21, Issue27July 3, 1990 RelatedInformation

Infrared Study of Hexahydrophthalic Anhydride, Halogenated Phthalic Anhydrides, Halogenated Maleic Anhydride and Styrene-Maleic Anhydride Copolymer in Solvent Mixtures

The v(C=O)2 modes for carboxylic acid anhydrides decrease in frequency as the solvent solubility parameter value increases. The vout-of-phase(C=O)2 mode for anhydrides decreases more in frequency than the vin-phase(C=O)2 mode in going from CCl4 solution to CHCl3 solution, indicating that it is more difficult for the vout-of-phase(C=O)2 mode to vibrate than it is for the vout-of-phase(C=O)2 mode in the same solvent system. Solute/solvent interaction induces a change in the Fermi resonance interaction between v(C=O)2 and combination and/or overtones of lower-lying fundamentals as the mole % solvent 1/solvent 2 changes.

Temperature dependences of intra- and inter-molecular interactions in water and 12-Crown-4 - a comparison

Intra-, inter-molecular (inter-bond) and Fermi resonance interactions in water and 12-Crown-4 are considered. The temperature dependences of the corresponding interaction constants, recently published in literature (Refs. 1,2), are compared. It is shown that the main reason for the existing differences in the temperature behaviour of the intramolecular and Fermi resonance interactions between water and crown is the presence of strong temperature dependent H bonds between water molecules and an absence of such or similar bonds between crown molecules. The similarity in the temperature behaviour of the intermolecular (interbond) interaction in water and in crown is because of the similar mechanisms of the intermolecular (interbond) coupling.

A study of vibrational anharmonicity, fermi resonance interactions, and local mode behavior in CH 3Cl

The infrared spectrum of CH 3Cl has been studied up to 16 500 cm −1 and vibrational assignments made for up to six quanta of excitation in CH stretching. Analysis of a total of 66 vibrational levels has been made in terms of a joint local mode and normal mode model, local with respect to CH stretching vibrations and normal with respect to other vibrations. Fermi resonance interactions with CH 3 deformation overtones must be included in the analysis. Reproduction of the observed vibration levels with a rms error of 2.61 cm −1 is achieved in terms of a 37-parameter model, with the four anharmonicity constants and two Darling-Dennison constants associated with CH 3 group stretchings constrained to be interrelated through local mode relations. The parameters obtained are in excellent accord with those available for the other methyl halides, and with established structural differences between the molecules.

Solvent-Induced Carbonyl Frequency Shifts: Cyclopentanone and Cyclohexanone

The carbonyl stretching vibration, vC=O, for cyclopentanone is in Fermi resonance with a combination tone, and the amount of Fermi resonance interaction between these two modes is dependent upon the amount of solute/solvent interaction. Correction for Fermi resonance shows that vC=O for cyclopentanone decreases in frequency by approximately 17.1 cm−1, progressing in the series of solvents from hexane through methyl alcohol. In the same series of solvents the vC=O frequency for cyclohexanone decreases in frequency by approximately 22 cm−1, progressing through the series of solvents hexane through methyl alcohol. Moreover, the vC=O mode for cyclohexanone occurs at a lower frequency than the vC=O mode for cyclopentanone (after correction for Fermi resonance) by between 26.5 and 33.2 cm−1, depending upon which particular solvent was used to dissolve cyclopentanone and cyclohexanone. The larger decrease in frequency for vC=O of cyclohexanone compared to vC=O for cyclopentanone in the same series of solvents is attributed to the fact that the (CH2)5 group contributes more electrons to the C=O group than does the (CH2)4 group. Consequently, the carbonyl group for cyclohexanone is more basic than the carbonyl group for cyclopentanone. Thus, there is a larger solute/solvent interaction in the case of cyclohexanone than in the case of cyclopentanone. The solvent acceptor numbers do not correlate well with the vC=O frequencies for either cyclohexanone or cyclopentanone (ACFFR).

Infrared Study of Maleic Anhydride in Solvent Systems

The out-of-phase (C=O)2 stretching mode for maleic anhydrides, vout-of-phase (C=O)2, is in Fermi resonance with a B1 combination tone, and the extent of Fermi resonance interaction can be altered drastically depending upon the particular solvent system used in the study. The vout-of-phase (C=O)2 and vin-phase (C=O)2 modes can be differentiated by solvent system studies, since the out-of-phase mode shifts more in frequency than the in-phase mode. Both v(C=O)2 modes decrease in frequency as the polarity of the solvent system increases or the amount of intermolecular hydrogen bonding increases, such as in the case of an increasing mole % concentration of chloroform.

Fermi resonance and solvent dependence of the CO moiety of 4‐(dimethylamino) benzaldehyde

AbstractThe Raman spectra of 4‐(dimethylamino)benzaldehyde in the 1550–1750 cm−1 region in seventeen solvents and as a molten liquid were measured. In all cases a multicomponent band was observed in the CO stretching region and these components were analyzed by the solvent variation method for Fermi resonance interactions. Unperturbed vibrational frequencies were calculated, and the frequencies attributed to ν(CO) were plotted against the solvent electron acceptor, number. A dual‐trace plot was observed. These traces were attributed to extrinsic interactions involving both the carbonyl oxygen and the aldehydic hydrogen in solvents of low acceptor number and predominantly the carbonyl oxygen in solvents of high acceptor number. The spectrum of molten 4‐(dimethylamino)benzaldehyde was used to predict an acceptor number of 14 for this molecule. This value was used to differentiate between high and low acceptor numbers for the solvents used in this study.

Fermi Resonance Variability Induced by Solute/Solvent Interaction: Phthalic Anhydride

The amount of Fermi resonance (F.R.) interaction between vo.p. (C=O)2 and a combination tone of phthalic anhydride varies systematically with change in the volume percent ratios of the solvents such as CHCl3/CCl4 and (CH3)2SO/CCl4. Correction for F.R. shows that vo.p. (C=O)2 decreases 5.2 cm−1 while the combination tone increases 3.2 cm−1 in going from CCl4 solution to CHCl3 solution. At 23.1 volume % CHCl3/CCl4, the bands in F.R. (1789 and 1776 cm−1) have equal intensity, and in this unique case both bands result from equal contributions from vo.p. (C=O)2 and the combination tone. The solute/solvent interaction in the (CH3)2SO/CCl4-phthalic anhydride system is even larger than that for the CHCl3/CCl4-phthalic anhydride system.

Fermi resonances between CH stretching and bending vibrations in CHF3, CHCl3, and (CF3)3CH

A simple vibrational curvilinear internal coordinate Hamiltonian is used to account for Fermi resonance interactions between CH stretching and bending vibrations in CHF3, CHCl3, and (CF3)3CH. The eigenvalues of the Hamiltonian are obtained variationally with a Morse oscillator basis set for the stretch and two-dimensional harmonic oscillator basis set for the bend. Five or six potential energy parameters are found to describe well the experimental CH stretching and bending overtone levels of the studied molecules. In the case of CHF3 the potential energy surface obtained is in good agreement with ab initio surfaces. A bond dipole model is used to calculate infrared absorption intensities for the transitions from the ground state to the totally symmetric excited states.

The quantum Henon–Heiles problem with Coriolis coupling: A comparison of algebraic and exact results

The results of an algebraically computed double Van Vleck perturbation theory are reported for combined anharmonic and Coriolis perturbations to a degenerate harmonic oscillator. The results to sixth order in the anharmonic coupling and comparable Coriolis coupling are in excellent agreement with exact calculations for systems with anharmonic splittings of up to 5% to 10% of the vibrational spacing. Particular care is required in handling Fermi resonance interactions in the algebraic computations.

Concentration (D2O in H2O) and temperature Raman study of the molecular interactions in the OD stretching spectra of D2O and D2O/H2O mixtures using the fourier deconvolution technique

AbstractThe OD stretching spectra of D2O for temperatures from 5 to 90°C and for concentrations (D2O in H2O) from 100 to 10 mol‐% were studied. These spectra were treated by means of the Fourier deconvolution technique for the first time.Using the positions of the resolved components the coupling constants for intra‐ and inter‐molecular and Fermi resonance interactions and all parameters according to the presented model, for all investigated temperatures, were evaluated. A gradual decrease in all interactions was observed in the concentration study, in accordance with expectations and in agreement with the results for dilute solutions of H2O in D2O.The temperature behaviour of the coupling constants and other parameters were in accordance with the corresponding data for H2O. The only exception is the temperature behaviour of the intramolecular coupling constant. The greater mass of the D atom is one of the probable reasons that lead to the smaller sensitivity of OD frequency to the hydrogen bond fluctuations.All the results verify the assignments and assumptions made according to the model presented and support the continuous model for the water structure.

Temperature study of intra‐ and inter‐molecular coupling and Fermi resonance constants in the Raman spectra of liquid water using Fourier deconvolution

AbstractThe structure of the Raman OH stretching band of water has been investigated from 4 to 90 °C using a Fourier deconvolution technique. The overlapped components in the isotropic and anisotropic spectra have been resolved. The information on the positions of the components in the deconvoluted spectra was used for calculation of the constants for intra‐ and inter‐molecular coupling and Fermi resonance and for an estimation of the component frequencies according to the model presented. For the first time, the value of the asymmetric Fermi resonance constant and the temperature dependences of all coupling constants have been obtained. Their temperature behaviour is in good agreement with the data in the literature concerning the different phases of water. It was established that the intramolecular coupling constant increases and the intermolecular coupling constant decreases as the temperature increases. The Fermi resonance constant for symmetric components tends to decrease with increasing temperature. The decrease in the symmetric Fermi resonance interaction with increasing temperature is due to the increase in the distance between the unperturbed fundamental and overtone band positions. The asymmetric Fermi resonance constant tends to increase with increasing temperature and this determines the strengthening of the asymmetric Fermi resonance interaction, which exhibits a limiting value at high temperatures.

Concentration Raman study of intramolecular, intermolecular and Fermi resonance interactions in the OH stretching spectra of dilute solutions of HDO in D2O using Fourier deconvolution technique

The Raman OH stretching spectra of dilute solutions of H20 in D20, from 100 mole per cent to 10 mole per cent concentration, are studied. For the first time the decoupled OH spectra are treated by means of Fourier deconvolution technique. The resolved components in the isotropic and anisotropic spectra are analysed in terms of a model. The frequency and intensity behaviour of the components confirm the suggestion, that strong decoupling of all vibrations with dilution takes place. It is shown that intramolecular and Fermi resonance interactions are negligibly small under 20 mole per cent concentration. On the contrary, a significant intermolecular interaction, with a coupling constant equal to 42 cm−1, is observed down to concentrations of 10 mole per cent. The latter is explained with the significant number of the HDO molecules, which have at least one HDO, or H20 neighbour at this concentration. In respect to intermolecular interaction a dilution of H20 in D20 down to 10 mole per cent concentration is e...

Effects of orbital angular momentum in CH2The Renner-Teller effect

The vibrational and K-type rotational levels of the a 1 A 1 and the [btilde] 1 B 1 state of CH2 have been fitted by least squares to give a pair of Born-Oppenheimer potential curves for the combining electronic states. An accurate description of the effects of orbital angular momentum on the energy level positions has been obtained. We have been able to relate the force constants used in the calculation of the bond length variation in the semi-rigid bender model to the parameters derived from the deperturbation of the Fermi resonance interaction, and have shown that there is reasonable agreement between them. Finally we have been able to link the amount of unpaired angular momentum ⟨Lz ⟩ produced by the vibronic coupling to the degree of magnetic activity observed in the vibronic sub-bands, and in rotational energy levels of the a, v 2 = 0 state.

Structural aspects of the effect of pressure on the Raman and infrared spectra of n-hexadecane

Raman and infrared spectra of neat n-hexadecane were measured as a function of hydrostatic pressure up to 54 and 83 kbar, respectively. The application of high pressure leads to anomalous frequency shifts and band splittings, and induces drastic changes in the band shapes and in the distribution of intensities within the spectra. The pressure-induced changes in the vibrational spectra of n-hexadecane are discussed in terms of phase transitions, molecular distortions, interchain interactions, frequency dispersions, and Fermi resonance interactions. The effect of pressure on the Raman and infrared spectra of n-hexadecane is used to test conclusions drawn from theoretical Fermi resonance calculations concerning the origin of several features in the Raman spectra of n-alkanes. Evidence is given to show that some assumptions made in these calculations are incorrect and that the model used is too simple to account for the intensity distribution in the CH stretching region of the Raman spectra of n-alkanes. It is also shown that the peak heights of the 2930 and 2850 cm−1 Raman bands can be affected by such factors as the magnitude of interchain interactions which renders questionable the use of the peak height ratio between these bands for the quantitative estimation of the gauche/trans population in biomembranes and polymers. While hydrostatic pressure initially causes a conformational ordering of the chains in n-hexadecane, at high pressures the compression along the chain direction is predominant over the lateral compression, leading to a distortion of the methyl end groups and a conformational disordering of the methylene chains.

Temperature-dependent fermi resonance studies and lineshape simulation by random perturbation model

The lineshapes of Fermi diads of thioacetamide and methyl thiourea have been measured at different temperatures in the 120–300 K range. For computation of the lineshape, the dynamic part of the Fermi resonance interaction has been considered as a random perturbation by Redfield's theory. The optical Bloch equations are set up including the Redfield relaxation terms. The steady state solution of these equations lead to the absorption spectrum. The computed lineshape of a Fermi diad is shown to be a superposition of two Lorentzians and an interaction term. The linewidth of the Lorentzians are controlled by the Redfield and 1/ T 2 relaxation terms. The comparison of the computed curves with the observed spectra demonstrates the importance of the dynamic part of the interaction on the lineshape.

Tuning of the Fermi resonance of CO2 and CS2 by temperature, pressure, and matrix material

The influence of temperature, pressure, and matrix material on the Fermi resonance interaction of the molecular crystals CO2 and CS2 is investigated. The anharmonic constant κ122 and the unperturbed energy difference Δ are calculated from the experimental energy and intensity data. The sharp Fermi resonance of CO2 is mainly influenced by the change in unperturbed energy difference with a constant anharmonicity, while the tuning of the weak resonance of CS2 is also driven by changes in κ122. Moreover, the variation of the Fermi resonance quantity Δ is changed by the usual solid, temperature, pressure, and matrix shifts of the energy levels. Although the fundamental ν2 should be independent of the Fermi resonance interaction it shows an unusual behavior, which is influenced by its overtone 2ν2 and driven by the tuning of the Fermi resonance. A decrease of Fermi resonance is observed on the gas–solid transition, when increasing temperature and on increasing pressure. An increasing Fermi resonance, produced by an elevation of environmental symmetry and increasing lattice size, realized by matrix-isolated studies, is only significant for the smaller resonance of CS2. For matrix-isolated CO2 a decrease of Fermi resonance is noticeable only in the nitrogen matrix.

Infrared spectroscopic studies of hydrogen bonding in triethylammonium salts. Part 4.—Rearrangement of hydrogen-bonded ion pairs of triethylammonium salts caused by interaction with tetrabutylammonium salts in solution

Rearrangement of triethyl-and tetrabutyl-ammonium salts in chloroform solution has been revealed from the characteristic features of the ν(N+H) bands caused by Fermi resonance interaction. Temperature changes of the i.r. spectra show this process to be reversible. Rearrangement constants K1 and K–1 and enthalpies –ΔH(for some cases only) of this process have been determined by measuring the total integrated intensities of the ν(N+H) bands of complexes which are in equilibrium. K1 values of the tetrabutylammonium salts increase with decreasing hydrogen bonding strength in triethylammonium salts. The measured enthalpies of rearrangement and those calculated from the ν(N+H) bands of hydrogen-bonded complexes studied are in agreement. It has also been shown that tetrabutylammonium salt anions can participate in the rearrangement of hydrogen-bonded ion pairs like the organic bases studied previously.