Analysis of Coriolis perturbations in the high-resolution infrared spectra of arsine (AsH3)

Numerical methods for the analysis of high-resolution infrared spectra of symmetric top molecules perturbed by Coriolis interactions between degenerate and nondegenerate vibrational levels are discussed in the second order of approximation. Application to the high-resolution infrared spectra of the AsH₃ molecule in the region of the fundamentals ν₁, ν₃ and ν₂, ν₄ yields considerably improved values of the molecular constants of AsH₃, including the band origins rotational constants, Coriolis coupling constants, centrifugal distortion constants, and the parameter of the K-type doubling effect.     

Coriolis interaction between ν4 and ν6 in the infrared spectrum of HCOF

The present work reports infrared gas spectra of the ν₄ and ν₆ perpendicular bands of HCOF. The vibration-rotation bands have been analysed in the rigid symmetric top approximation. The rotational structure is explained in terms of Coriolis perturbations between these fundamentals. Two possible assignments are given for ν₆; the values of the Coriolis coupling constant for both assignments are equal within the accuracy of the experiment.     

Torsional Line Splittings in the (ν4+ν8)−ν4 Hot Transitions of C2H6 between 1400 and 1510 cm

A detailed investigation of the high-resolution infrared spectrum of ethane revealed the occurrence of features belonging to the hot perpendicular system (ν₄+ν₈)−ν₄ between 1400 and 1510 cm⁻¹. Transition lines of the subbranches with K″ΔK from −7 to 4, exhibiting torsional splittings of several tenths of a cm⁻¹, were observed and measured in this region. The observed line splittings are strongly influenced by the interaction between the ν₄+ν₈ and 2ν₄+ν₁₂ states and change with the values of K″ΔK, depending on the zero-order energy separation of the interacting levels. We found by numerical extrapolation that splittings still occur far from resonance, showing that the intrinsic torsional splittings of the combining states ν₄+ν₈ and ν₄ are quite different. We determined the intrinsic torsional splitting of ν₄+ν₈ to be less than 0.083 cm⁻¹, compared with 0.236 cm⁻¹ estimated for the ν₄ state. This result is in agreement with the expected effects of torsional Coriolis and head-tail coupling and is consistent with previous observations on vibrationally degenerate states of ethane-like molecules.     

Effective charge of divalent lead: Application to the assignment of infrared modes in ferroelectric Pb5Ge3O11

A correlation between Szigeti effective charge and the electronic polarizability is found for the eight compounds containing divalent lead where experimental data are available. Results in Pb₅Ge₃O₁₁ contribute to remove some ambiguity about the assignment of polar vibrational modes as external or internal to GeO₄ and Ge₂O₇ entities in ferroelectric lead germanate. Complete TO-LO splittings are also deduced from infrared reflection spectra obtained at room temperature. Results are compared with previous controversial Raman measurements of the polar character of the modes including the soft mode.     

The effective Hamiltonian for the coupling between inversion-torsion states in methylamine

The Hougen’s formalism of group-theoretical effective Hamiltonian has been extended to include the resonances between the wagging, ν₉, and third or fourth excited torsional, 3ν₁₅ and 4ν₁₅, states in methylamine. The presented Hamiltonian treats explicitly these couplings. For each of these bands the rovibrational sublevels belong to all symmetry species of the G₁₂ group of methylamine. On the other hand the vibrational states for ν₉ and 4ν₁₅ are symmetric with respect to reflection in the symmetry plane of the NH₂ group, and antisymmetric for 3ν₁₅. We have shown that the coupling terms between the ν₉ and 3ν₁₅ states are limited to Coriolis-like coupling, and no Fermi-type interactions are allowed. For the coupling between the ν₉ and 4ν₁₅ states all kind of interaction terms are possible.     

On the Study of Resonance Interactions and Splittings in the PH3 Molecule: ν1, ν3, ν2+ν4, and 2ν4 Bands

The high-resolution (0.005 cm⁻¹) Fourier transform infrared spectrum of PH₃ is recorded and analyzed in the region of the fundamental stretching bands, ν₁ and ν₃. The ν₂+ν₄ and 2ν₄ bands are taken into account also. Experimental transitions are assigned to the ν₁, ν₃, ν₂+ν₄, and 2ν₄ bands with the maximum value of quantum number J equal to 15, 15, 13, and 15, respectively. a₁-a₂ splittings are observed and described up to the value of quantum number K equal to 10. The analysis of a₁/a₂ splittings is fulfilled with a Hamiltonian model which takes into account numerous resonance interactions among all the upper vibrational states.     

Vibrational spectra of crystalline H2SeO3 in the O-H stretching region

IR transmission, near-normal IR reflection and polarized Raman spectra of single crystals of selenious acid (H₂SeO₃) have been obtained at temperatures between 77°K and 335°K. The observed bands in the O-H stretching region have been assigned to two types of O-H….O bonds in the crystal structure. The spectral results appear to rule out correlation field splittings, intramolecular coupling, or Fermi resonance as explanations for the observed splitting. A proposed model based on intermolecular coupling of O-H….O vibrations to explain the splitting of the O-H stretching region is given.     

The ν5 perpendicular band of deuterated fluoroform

The results of an infrared diode-laser-heterodyne investigation of the ν₅ band of deuterated fluoroform (CDF₃) are presented. Infrared heterodyne measurements (410), together with the previously obtained 88 infrared laser-Stark measurements, 12 infrared-radiofrequency, two-photon measurements, 8 microwave measurements, and 22 submillimeter-wave heterodyne measurements were analyzed by linear least-squares fitting of the data with a 43-constant linear Hamiltonian. Most of the ground-state and ν₅-state constants are obtained to very high accuracy, and the fit to the data is excellent. Examination of the data reveals effects such as A₊-A_? splittings and perturbation-allowed transitions arising from the mixing of kl = 1 and kl = ?2 levels in the ν₅ state due to (±2, ±1) interactions.     

Two-band BCS mechanism of superconductivity in a Ba(Fe0.9Co0.1)2As2 high-temperature superconductor

Terahertz and infrared spectra of the conductivity, σ(ν), and dielectric constant, ?(ν), of a Ba(Fe_0.9Co_0.1)₂As₂ film (T _c = 20 K) have been analyzed together with previous specific-heat and angular resolved photoelectron spectroscopy data. It has been shown that the spectra σ(ν) and ?(ν) of Ba(Fe_0.9Co_0.1)₂As₂ in the superconducting phase at T = 5 K, as well as the magnetic field penetration depth, can be described well using the standard Bardeen-Cooper-Schrieffer (BCS) model with an additive contribution of electron and hole bands. It has been found that the measured temperature dependence of the magnetic field penetration depth in a wide temperature range 5 K < T < T _c can be described only with the introduction of interband pairing interaction. The coupling constant of electron and hole bands, λ_{1, 2} = 0.1, as well as the temperature dependences of superconducting gaps in the electron and hole subsystems, has been determined using the model of two-band superconductivity developed earlier for MgB₂.     

Specific features of the reflection of infrared radiation by crystalline dielectrics in a magnetic field

Magnetic-field-induced variations in the reflection spectra R(λ) of the crystalline dielectrics Al₂O₃, LiF, and MgO in the infrared band (λ = 2.5–25 μm) are investigated. It is found that the reflection spectra exhibit specific features in the neighborhood of wavelengths corresponding to the excitation of optical phonon modes in the above-mentioned crystals and that a magnetic field causes an appreciable variation in the reflectivity at these wavelengths. To qualitatively describe the effect of a magnetic field on the reflection of light, the magnetoreflection spectra ΔR/R are investigated. The spectra ΔR/R exhibit sharp peaks in the neighborhood of wavelengths at which the materials under investigation are characterized by minimal reflectivity. The values of ΔR/R for p-polarized infrared radiation in a magnetic field of about 12 kOe amount to about 0.5% for Al₂O₃ at λ ≈ 9.6 μm, 7% for LiF at λ ≈ 11.1 μm, and 0.07% for MgO at λ ≈ 11.7 μm.     

The Raman spectrum of solid cyclopropane

The Raman spectrum of polycrystalline cyclopropane between 3200 and 10 cm^?1 has been recorded. All Raman active fundamentals, two other fundamentals ν₄(A″₁) and ν₇(A″₂), several new crystal components of fundamentals, and many new bands arising from overtones and combinations have been observed.The splittings of the fundamentals, together with the coincidences of infrared and Raman wavenumbers for both fundamentals and lattice modes, are consistent with a C_2v factor group, a C_s site, and two molecules per orthorhombic unit cell.     

Microwave spectrum of methylene fluoride in excited vibrational states

The rotational spectra of ¹²CH₂F₂ in seven of the nine fundamental vibrational states and also in overtone and combination states involving the ν₄ mode were observed and assigned. Coriolis interactions between ν₃ and ν₇, ν₂ and ν₈, ν₃ and ν₉, and ν₅ and ν₇ were analyzed by using approximate expressions for the rotational levels. An effective Hamiltonian with the Coriolis term in the off-diagonal block was applied to stronger interaction between ν₃ and ν₉. Fermi resonance between ν₃ and 2ν₄ was found to be negligible. The ground state spectra of ¹²CH₂F₂ and of ¹³CH₂F₂ were remeasured to improve the accuracy of the rotational and centrifugal distortion constants. The Coriolis coupling constants and the energy differences between two vibrational levels in resonance, which were obtained through an analysis of the satellite spectra, are compared with the results derived from a normal coordinate analysis.     

The absorption of ethylene in the 10-μm region

The ν₇, ν₁₀, and ν₄ interacting band system has been studied from three complementary sources: classical, diode laser, and waveguide laser spectra. In addition to the two first-order Coriolis interaction terms associated with ζ_7.10^a and ζ_4.10^b, we were obliged to introduce the corresponding second-order terms to obtain a statistical agreement between calculated and experimental data. High-quality vibrational and rotational data are presented for the two infrared active fundamentals, ν₇ and ν₁₀, and the rotational constants for the inactive ν₄ fundamental are determined for the first time. We also present the list of all the infrared transitions starting from the vibrational ground state of ethylene and being in quasi coincidence with CO₂ or N₂O laser lines.     

Vibrational spectra dihalogenated benzenes. I. In-plane vibrations

Infrared and Raman spectra of D₄-ortho, meta and para fluorochloro and fluorobromo benzenes are presented and assignments are given. Some of the bands of H₄-p-fluorochloro benzene assigned earlier as fundamentals are shown to be due to impurities and alternate assignments are given. The observed frequencies of the H₄ and D₄ molecules are combined in a normal coordinate analysis to obtain a 33-parameter modified valence force field, for the in-plane vibrations, with an average difference of ±0.8% between observed and calculated frequencies. The normal coordinate analysis shows that many of the previous assignments of the ring modes ν₁, ν₆, and ν₁₂ for disubstituted benzenes are not very reliablie. Revised assignments with good correlation with the corresponding benzene modes are given.     

Doppler-limited spectra of the ν3 vibration of 12CH4 and 13CH4

The tetrahedral splittings in the P and R branches of the ν₃ band of natural methane have been examined with Doppler-limited resolution using a difference-frequency spectrometer. The spectra obtained by this difference-frequency mixer are compared to recent high-resolution grating spectrometer studies of ¹²CH₄ and enriched ¹³CH₄. The resolution, selectivity and precision are improved over the conventional methods. The mixing spectrometer utilizes tunable, narrow linewidth infrared radiation generated in the nonlinear optical crystal, LiNbO₃ as the beat frequency between a CW argon ion and a tunable dye laser. This spectrometer covers the 2.2 to 4.2 μm infrared spectrum with an instrumental resolution of 5 × 10^?4 cm^?1 and continuous scans up to ～1 cm^?1 and with ir power ～1 μW.     

The gas phase Raman band contours of 1,3,5-trifluorobenzene and the infrared and Raman band contours of 1,3,5-trifluorobenzene-d3

The gas phase infrared and Raman spectra of 1,3,5-trifluorobenzene-d₃ has been recorded. The gas phase Raman spectrum of 1,3,5-trifluorobenzene-h₃ has also been recorded. Computer simulations of the band contours of the degenerate vibrational modes have been used to determine the first-order Coriolis coupling constants for both molecules. The ζ^z values were then compared with those evaluated from force field calculations.     

Infrared spectra of 1-phosphapropyne,CH3CP,and its perdeuteride,CD3CP

The infrared spectra of 1-phosphapropyne, CH₃CP, and its perdeuteride, CD₃CP, have been measured in the gaseous and solid states. The Q_K branches of perpendicular bands have been analyzed in terms of the usual quadratic expression in K. Fermi resonances were identified for the ν₁, ν₂ + ν₃, 2ν₃, 2ν₆⁰; and ν₅, 2ν₃ + ν₈ band systems of CH₃CP and the ν₁, 2ν₃, 2ν₆⁰; ν₆, ν₇ + ν₈; and ν₇, 3ν₈¹ band systems of CD₃CP. The xy Coriolis interaction was also identified between the ν₃ and ν₆ bands of the two species. All the fundamentals were assigned and the normal coordinate treatment was carried out along with the Coriolis constants, ζ^z.     

Analysis of the ν1 and ν2 + ν4 bands of 12CH4

Line assignments, positions, strengths, and experimentally determined upper states are reported for the ν₁ and ν₂ + ν₄ infrared bands of ¹²CH₄. The bands have been analyzed using infrared spectra recorded with different optical densities and temperatures at 0.02- and 0.01-cm^?1 resolution using a four-passed grating spectrometer at Florida State University and a Fourier transform spectrometer at Kitt Peak National Observatory. Both ν₁ and ν₂ + ν₄ lines are assigned through J′ = 14. For J′ ≥ 10, the upper state of the vibrationally infrared inactive ν₁ band interacts strongly with ν₂ + ν₄ and is observed in the infrared spectrum with line strengths on the order of 10^?3 cm^?2 atm^?1. The upper-state energies and transition intensities are calculated from the molecular constants and transition moment matrix elements obtained through a simultaneous analysis of ν₁, ν₃, ν₂ + ν₄, 2ν₄, and 2ν₂.     

Infrared spectra of AlF3 in solid argon

Three infrared absorptions are assigned to AlF₃ isolated in solid argon: ν₂ = 286.2 cm^?1, ν₃ = 909.4 cm^?1, and ν₄ = 276.9 cm^?1. The multiplet pattern previously reported near 950 cm^?1 is not present in carefully isolated AlF₃. Our spectra do not conclusively rule out a pyramidal structure for AlF₃; however, no infrared absorptions can be confidently assigned to ν₁, the symmetric stretch.     

Microwave spectrum of methylene fluoride-d2, CD2F2 in the excited vibrational states

The rotational spectra of ¹²CD₂F₂ in the ν₂, ν₃, ν₄, 2ν₄, ν₅, ν₇, ν₈, and ν₉ states were observed and assigned. Weak Coriolis interactions between ν₃ and ν₇, ν₃ and ν₉, and ν₅ and ν₇ were analyzed using approximate expressions for the rotational energy levels. The resonance between the ν₂ and the ν₈ state was found much stronger, and an effective two-dimensional Hamiltonian with the Coriolis term in the off-diagonal block was set up to analyze the spectra. The effect of the Fermi resonance between ν₃ and 2ν₄ was found to be very small.The ground-state spectrum of ¹³CD₂F₂ was observed and the rotational constants and the centrifugal distortion constants were determined. The data on ¹²CD₂F₂ and ¹²CDHF₂ were also improved very much in accuracy.The Coriolis coupling constants and the differences between two vibrational levels in resonance, which were determined by the analysis of the satellite spectra, are in good agreement with those obtained from vibrational spectra, except for the ν₂ band center, which is revised to 1170.3 cm^?1. The force constants were also checked using the centrifugal distortion constants of ¹²CD₂F₂, ¹³CD₂F₂, and ¹²CHDF₂.