Anharmonic Resonances Research Articles

Vibrational Assignment and Anharmonic Resonance Analysis of the Dispersed Fluorescence and Stimulated Emission Pumping Spectra of DFCO (S0) up to 9000 cm−1

Dispersed fluorescence and stimulated emission pumping spectra of jet-cooled DFCO from the 2162, 5164, 215162, and 5166vibrational states ofS1are presented up to 9000 cm−1. Progressions are assigned primarily to vibrational states with excitation in the Franck–Condon active modes ν2, ν5, and ν6. The spectrum is perturbed by a 266 (ν2≈ 2ν6), a 233 (ν2≈ 2ν3), and a 3566 (ν3+ ν5≈ 2ν6) anharmonic resonance. These three resonances are increasingly important at high vibrational energies, thus explaining the complexity of the DFCO spectrum compared to that of HFCO. Seventy-five vibrational states are assigned as eigenstates of a 266, 233, and 3566 anharmonic resonance Hamiltonian. The rms deviation in the calculated energies is 1.2 cm−1. Harmonic frequencies and anharmonic constants are reported. These are compared to constants derived fromab initiopotential energy surfaces.

Infrared Analysis of the Anharmonic Resonance between ν8+ ν9and the Dark State ν6+ ν7of HNO3

The high-resolution FTIR spectrum of the ν8+ ν9band of HNO3around 1205 cm−1has been measured and analyzed. The bright state was found to be strongly perturbed by its neighboring dark state ν6+ ν7at the coincident levels. Taking account of the ΔK= ±2 anharmonic resonance, a simultaneous fit of ν8+ ν9and ν6+ ν7was performed leading to a good reproduction of the ν8+ ν9band with a rms uncertainty of 0.00046 cm−1. A set of rovibrational constants for ν8+ ν9were accurately determined, while for ν6+ ν7the rotational constantBand the band origin were obtained.

Infrared Diode-Laser Molecular-Beam Spectrum of the ν2Band of Chlorine Nitrate at 1293 cm−1

The ν2band of chlorine nitrate (ClONO2) near 1293 cm−1has been measured in a molecular beam with a diode-laser spectrometer. The low rotational temperature of the molecular beam, ∼23 K, simplifies the spectrum allowing essentially complete assignment of the35Cl and37Cl lines. Ana/bhybrid band is observed with thea-type transition moment being approximately a factor of 2 larger than theb-type transition moment. An inverted shift of the band origins is found with the37Cl band origin blue shifted from the35Cl by +0.37 cm−1. This isotopic shift is attributed to an unidentified anharmonic resonance. Precise spectroscopic constants for the bands of each isotopic species are determined to allow future simulations for modeling atmospheric transmission and for remote sensing applications.

Vibrational spectroscopy of CH/NH stretches in pyrrole: An algebraic approach

The complete vibrational spectroscopy of pyrrole is addressed within the one-dimensional algebraic framework. Particular attention is devoted to the study of the CH/NH stretching levels, including their possible anharmonic resonance mechanisms with other ring modes.

Fourier Transform Infrared Spectrum of FCN: The 1800–2800 cm−1Spectral Range

The infrared spectrum of cyanogen fluoride (FCN) in the 1800 to 2800 cm−1region has been recorded with a Fourier transform spectrometer at an instrumental resolution of 0.0026 cm−1. A total of 6822 absorption lines have been measured with an accuracy better than 6 × 10−4cm−1. Forty-nine bands of19F12C14N, twelve of19F13C14N, and four of19F12C15N have been analyzed. For these bands, the band origins and rotational constantsBv,Dv,Hv, andLvas well asqv,qDv, andqare reported. We have also detected for the first time a perturbation in the 3000 vibrational state. This perturbation is interpreted as due to an indirect effect of the two first-order anharmonic resonances between 3000 and 0201.

Analysis of the Hot Bands ν7+ ν8− ν8and ν4+ 2ν8− ν8of Methyl Isocyanide

The perpendicular hot bands ν∓7+ ν∓8− ν∓8(E–E), ν∓7+ ν±8− ν±8(A1,2–E), and ν4+ 2ν±28− ν±8(E–E) occurring in the region of the ν7fundamental of CH3NC (1050–1250 cm−1, cf. J. Plı́vaet al., J. Mol. Spectrosc.173,423–430, 1995) have been analyzed. Eleven subbands of theE–Ecomponent and 10 subbands of theA1,2–Ecomponent of ν7+ ν8− ν8plus four subbands of ν4+ 2ν8− ν8have been assigned and used in the analysis. The fundamental states ν6and ν3which strongly affect the upper states of the hot transitions by anharmonic and Coriolis resonances have been included in a comprehensive analysis. Reliable values are reported for the spectroscopic and interaction constants of all the states involved as well as for the vibrational and anharmonic constantsx78,x78(g78),x48, ω08,x88, andx88(g88).

Fermi resonance structure and femtosecond quantum dynamics of a chiral molecule from the analysis of vibrational overtone spectra of CHBrClF

AbstractThe rovibrational spectra of bromochlorofluoromethane (CHBrClF) were measured at intermediate (0.1 cm−1) and high resolution (0.001 cm−1) between the far infrared (20 cm−1) and the visible range of the spectrum (14000 cm−1) by interferometric Fourier transform techniques and diode laser techniques in stationary samples and supersonic jets. All fundamentals and numerous combinations and overtone transitions could be assigned and their band positions and integrated strengths were determined. A quantitative interpretation of the complex multiple resonance structure of the CH chromophore spectra (about 50 assigned bands) is given in terms of an effective anharmonic CH‐stretching‐bending Hamiltonian and in terms of vibrational variational calculations on a 3‐dimensional grid using ab initio (MP2 and B3LYP) and empirically adjusted potential hypersurfaces for the CH chromophore normal coordinate subspace. The systematic analysis of anharmonic resonances of the alkyl CH chromophore in symmetric top (C3v) and asymmetric top (Cs) molecules is herewith extended to chiral molecules. We provide a detailed analysis of the chiral Cs symmetry breaking coupling in the effective Hamiltonian (coupling constant |k′sab| =(20 ± 10) cm−1) and in the potential (Csab and further terms) and their relationship. The implications for the femtosecond intramolecular dynamics for CHBrClF are discussed in terms of quantum dynamical results for time‐dependent populations, survival probabilities, wavepackets and also time‐dependent symmetries and their violations (formal a′ and a′′ species for vibrational Cs and l quantum number for vibrational C∞v symmetry). We have also developed an improved synthesis of CHBrClF, which is suitable for the preparation of large quantities (several mol) of the pure (racemic) compound, and have demonstrated enantiomer separation by gas chromatography.

Networks of anharmonic resonance systems in the rovibrational overtone spectra of the quasilinear molecule HCNO

AbstractThe infrared spectrum of fulminic acid, HCNO, has been measured in the range 700‐7000 cm−1 with a Bruker IFS 120 HR interferometer. More than 130 new vibrational levels have been identified. Power series coefficients of these levels are given. Each vibrational level with its rotational levels is locally or globally perturbed. It was possible to classify most of the interactions into a grand network of Coriolis‐ and/or Fermi‐type resonance systems by using the previously known basic resonance systems 00010/00002 and 00100/00004. In addition, a new basic resonance for HCNO could be identified in the system 00015/01000/00103. As a consequence of the many interactions many so called “resonance‐enhanced” rovibrational subbands have been assigned. The identification and partial analysis of the resonance systems have been carried out, first with the help of different presentations of reduced term values and second by determining the J‐value separation between e and f crossing points. In this paper, the resonance systems 01100/01004/00203/00115 and 00014/00110/00102, which are combinations of the above mentioned basic resonance systems, will be discussed. Some further resonance systems that can be deduced from these are discussed in detail, too.

Anharmonic resonances in monodeuteroacetylene ( 12C 2HD)

Published data on the Fourier transform spectrum of 12C 2HD in the overtone range, from Liévin et al. [Chem. Phys. 10 (1995) 419] and abbouti Temsamani and Herman [Mol. Phys. 79 (1993)], are revisited by taking into account the ( 1 255 ) anharmonic resonance. A dedicated Hamiltonian is used to build interacting clusters. New vibrational parameters are obtained which account for previously reported anomalous spectral features.

High Resolution FTIR Study of PF3in the 800–950 cm−1Region. The ν1and ν3Fundamental and ν2+ ν4Combination Bands

The FTIR spectrum of PF3has been recorded in the 750–950 cm−1range covering the fundamentals ν1(891.940 5 cm−1) and ν3(859.544 1 cm−1) and the combination band ν2+ ν4(834.055 7 cm−1) with a resolution of ca. 2.5 × 10−3cm−1. Furthermore, spectra of the 2ν2, 2ν2− ν2, (ν2+ ν4) − ν4, and (ν2+ ν4) − ν2bands were measured and analyzed. The vibrotational analysis of the ν1and ν3bands confirmed the presence of a Coriolisx,yresonance whose interaction parameter could be determined experimentally. A transition moment ratio μ1:μ3close to 0.7 has been deduced from a band contour simulation for a negative sign of the intensity perturbation μ1ζ1,3μ3. Furthermore, anharmonic resonance between ν3and ν2+ ν4was established, the strength of which is in agreement with an interaction constantW234= 2.86 cm−1as suggested by ab initio calculations. More than 5000 rovibrational transitions belonging to ν1, ν3, and ν2+ ν4were fitted together with all available pure rotational data, σ(Fit) of the IR data being 3.93 × 10−4cm−1. It was found thatqresonance within ν3induces an avoided crossing of thek[formula]= 1,A−with thek[formula]= −2,A−sublevel nearJ= 12. Its effects give rise to an irregularA1A2splitting ofP(PQR)3lines and theRQ0branch near the crossing. The equilibrium rotational constantsBeandCehave been determined, and their significance is critically assessed. An equilibrium structure,de(PF) = 1.560 99(14) Å and[formula]FPF 97.57(4)°, has been calculated.

Cyclopropane-d6: The C–D Stretching Bands ν6and ν8at High Resolution

The two infrared active C–D stretching bands ν6and ν8of C3D6were recorded on a large Fourier transform spectrometer with a linewidth close to the Doppler–Fizeau limit. The perpendicular band of theE′ vibration ν8near 2209.6 cm−1is found to be highly perturbed by anharmonic resonances with the states ν7+ 3ν14, ν7+ ν9+ ν14, and ν4+ ν10+ ν14, and by aJx,yCoriolis-type interaction with an unidentified[formula]state. In contrast, the structure of the parallel band of the[formula]vibration ν6near 2336.7 cm−1appears to be relatively unperturbed. Spectroscopic constants are reported for the two fundamentals and for some of the perturbers of the ν8state.

96/00004 The chemistry of transformation of disulfhydryl iron to iron disulfide in natural systems (letter)

The semi-stable HC4Cl molecule has been detected in the pyrolysis products of propyne and carbon tetrachloride mixtures. The rotational spectrum of the most abundant isotopologue HC435Cl has been investigated in the millimetre- and sub-millimetre-wave regions for the ground and 12 vibrationally excited states which approximately lie below 630 cm−1, namely (ν5ν6ν7ν8ν9)=(10000), (01000), (00100), (00010), (00001), (00020), (00002), (00003), (00004), (00101), (00011) and (00012). Transitions up to J=151←150 were measured for the ground state, allowing for a precise evaluation of the quartic and sextic centrifugal distortion constants D and H. The l-type resonances between the different sublevels of the bending states and the anharmonic resonance which couples the states ν5=1, ν8=2 and ν9=4 have been taken into account in the analysis of the spectra, which yielded precise determinations of the xL(99), xL(88), xL(89) and xL(79) anharmonicity constants and of the ϕ588 normal coordinate cubic force constant. Extensive measurements have also been performed for the HC437Cl isotopologue.

Study of the Midinfrared and CH-Stretching Regions of CH2[formula]13C[formula]CH2

Infrared spectra of [2-13C]allene (H2C[formula]13C[formula]CH2) between 1300 and 3300 cm−1covering the ν7, ν9+ ν11, 2 ν10, ν6, ν5, and ν8bands have been studied at a resolution of ca. 0.004 cm−1. Spectroscopic constants are derived from single subband analysis of these bands and various perturbations are discussed. A detailed analysis of the[formula]band system is performed from a model taking into account Fermi resonance between ν7and[formula]higher order anharmonic resonance between ν7and[formula]higher order anharmonic resonance between[formula]and rotationall-type resonances within ν9+ ν11. The 2ν10band has been analyzed using a model taking into account rotationall-type resonances within 2ν10and (x,y)-Coriolis interactions with ν4+ ν10and ν7+ ν11. Both analyses yield a number of spectroscopic constants for the levels included in the models as well as various interaction constants.

Absolute Intensities in 16O 12C 32S: The 2500-3100 cm −1

About 400 absolute intensities have been measured for six bands(5 Σ-Σ and 1 Π-Σ bands) of 16O 12C 32S in the region of the ν 1 + ν 3 band near 3.4 μm. The majority of these bands exhibit weak to very strong Herman-Wallis behavior as a result of various anharmonic and l-type resonances between the upper levels involved. The individual line intensities were treated in two different ways. First, they were fitted to usual effective formulae, leading to the band strengths and Herman-Wallis factors. Second, the line intensities in the five Σ-Σ bands were fitted to a model taking explicitly into account the various anharmonic and I-type resonances between the upper levels. This treatment showed that these resonances quantitatively explain to a large extent the Herman-Wallis behavior observed.

Fermi resonances in the one-dimensional algebraic model

The problem of describing in a systematic fashion anharmonic (Fermi) resonances is addressed in the framework of the one-dimensional vibron model. As a practical example, the resonating manifold of in-plane CH bending modes and CC stretching modes of the ethylene molecule is studied in detail.

High-Resolution Vibration-Rotation FTIR Spectrum of the 2ν4, ν1, 2ν1 and 3ν1 Bands of HCCBr

The infrared spectrum of a sample of natural monobromoacetylene (HCCBr) has been recorded with the Bruker IFS 120 Fourier spectrometer in the wavenumber region 1100-9800 cm−1 with a resolution close to the Doppler limit. The 2ν4, ν1, 2ν1, and 3ν1 band systems have been analyzed. Altogether, 24 vibrational bands belonging to the HCC79Br and 26 bands belonging to the HCC81Br isotopic species have been observed and rotationally assigned. An anharmonic resonance model based on rectilinear normal coordinate theory has been used to produce the vibrational assignments for the observed bands.

Infrared spectroscopy of the CH stretching modes of partially F-substituted benzenes. II. The fundamental spectrum of fluorobenzene

This work is part of a series aimed to investigate the fundamental and overtone transitions of the CH stretching modes in partially F-substituted benzenes. In this article we report the study of the fundamental transitions of fluorobenzene (C6H5F) in the wave numbers range from about 3000 to 3150 cm−1. The absorption spectrum has been measured through both a low-temperature opto-acoustic cell and a supersonic-beam opto-thermal spectrometer. The opto-thermal spectrometer enabled us to measure the detailed vibrational structure, providing the basis for an algebraic analysis of the fundamental CH transitions. We show, in particular, how benzene algebraic procedures must be modified for taking into account the effects induced by the substitution of one hydrogen atom with fluorine, i.e., (i) the reduction of symmetry and (ii) the frequency (chemical) shift due to the change of electron distribution. Moreover we include the contribution of anharmonic resonances between unperturbed CH stretching modes and overtone or combination bands of lower energy molecular vibrations.

The vibrational energy levels in acetylene 12C2H2: Towards a regular pattern at higher energies

We have gathered 122 known experimental data concerning the vibrational energy levels of acetylene, C2H2, up to 12 000 cm−1. We have fitted the data simultaneously to a model based on the clustering of the levels induced by a set of eight anharmonic resonances. That set is carefully built from the literature information on various isotopomers of acetylene. The model takes full advantage of the anharmonic pattern and systematically block diagonalizes the entire vibrational energy matrix. The 122 input energies are reproduced within a standard deviation of 0.74 cm−1 with 35 fitted parameters. Decisive support to the model is brought by using the resulting vibrational parameters and matrix eigenvectors to reproduce energies, principal rotational parameters, and relative intensity features. The cluster picture is discussed, in terms of the 7 normal modes of vibration in acetylene, according to the theoretical model developed by Kellman [M. E. Kellman and G. Chen, J. Chem. Phys. 95, 8671 (1991)].

Quartic anharmonic resonances in acetylenes and haloacetylenes

Formulas are derived for the quartic anharmonic resonance coefficients observed to be important between C–H stretching and the combination of one quantum of C≡C stretching and two quanta of H–C≡C bending in a number of acetylene molecules. Examples of this resonance are ν3 with ν2+ν4+ν5 in 12C2H2, ν1 with ν2+2ν5 in 13C2H2, and ν1 with ν2+2ν4 in monofluoroacetylene and monochloroacetylene. The coefficients characterizing the resonances in these examples, which we denote K3,245, K1,255, and K1,244, arise from cubic and quartic terms in the anharmonic force field, in the normal coordinate representation, through second order and first order perturbation treatments respectively, where the second order resonances are calculated by a Van Vleck resonance formalism. The experimentally determined values of these coefficients are compared with values calculated from model anharmonic force fields.

Theoretical Approaches to Anharmonic Resonances

AbstractFour theoretical models for the treatment of anharmonic resonances are discussed, and one particular curvilinear approach is generalized. Theoretical resonance parameters for three of these models are calculated on the basis of ab initio anharmonic force fields. They are compared with experimentally derived effective resonance parameters and with other published theoretical data. 25 anharmonic resonances in 16 different molecules are covered, including the stretch‐bend Fermi resonances in the haloforms CHX3 and the methyl halides CH3X(X = F‐I). These comparisons suggest guidelines for the theoretical treatment of resonances.