Pressure broadening of methane lines in the 6190Åand 6825Åbands at room and low temperatures

Measurements of pressure broadened half-widths have been performed for one vibration-rotation line in the 6190Åmethane band and one vibration-rotation line in the 6825Åmethane band. Self-, nitrogen-, hydrogen- and helium-broadening have been measured over a temperature range of 77–295 K. Pressure broadening coefficients and temperature dependence indices have been obtained for each line and broadening gas.     

Non-LTE spectral absorption coefficients for vibration-rotation bands of diatomic molecules

Analytical expressions have been derived for the average non-LTE spectral absorption coefficients and the associated spontaneous emission coefficients of fundamental vibration-rotation bands of anharmonic oscillators. Relatively simple differential expressions are provided for the important practical conditions under which the smeared-rotational-line approximation is applicable and for which at least individual rotational temperatures exist for each pair of vibrational levels of interest.     

A new approach to obtaining sum rules

A new approach to obtaining the sum rules satisfied by the phenomenological coefficients appearing in the metric tensor of the generalized coordinate space of a many-particle system is considered and applied to the vibration-rotation motion of a nonlinear molecule. The approach is based on the requirement of physical covariance of the Cartesian and generalized coordinate configuration spaces of the system. A partial criterion of this physical covariance is the condition that the curvature tensor of configuration space remains covariant, and this condition gives several sum rules for the vibration-rotation parameters. These sum rules are particular cases of those known previously.     

Improved Parameterization for Combined Isotopomer Analysis of Diatomic Spectra and Its Application to HF and DF

A new way of representing vibration-rotation term values for multiple isotopomers of a given electronic state of a diatomic molecule is presented which resolves problems associated with the way the conventional combined isotopomer expansion represents the atomic mass-dependent JWKB and Born-Oppenheimer breakdown correction terms. Its application to infrared and microwave data for HF and DF yields new Dunham expansion coefficients and Born-Oppenheimer breakdown correction terms for this species. This procedure is implemented in a generally available computer program for fitting to various types of data involving one or several electronic states of multiple isotopomers of a diatomic molecule. Copyright 1999 Academic Press.     

Sequential contact transformation formulation of asymmetric-rotator vibration-rotation Hamiltonian

The sequential contact transformation technique recently described in this journal by Niroomand-Rad and Parker is applied to the Amat-Nielsen expansion of the Darling-Dennison Hamiltonian of asymmetric rotator type molecules. The resulting formalism for the calculation of fourth-order Hamiltonian coefficients is significantly simpler than the conventional Amat-Nielsen contact transformation formalism. Therefore the eventual development of detailed expressions for fourth-order vibration-rotation interaction coefficients in terms of fundamental molecular constants now appears much more feasible.     

Relative spectral absorption coefficients for the fundamental vibration-rotation bands of AlO

Relative spectral absorption coefficients have been calculated for the fundamental vibration-rotation bands of AlO between 2000 and 3500 K in the smeared-line approximation. A differential expression is given for the spectral absorption coefficient of individual vibration-bands, which is convenient for applications requiring integrations over finite wavenumber intervals.     

Nitrogen-induced broadening and shifts of rotation-vibrational lines in the fundamental, first, second and third overtone bands of HI

We report experimental results on the previously unknown broadening and shifting coefficients in the fundamental and three overtone vibration-rotation bands of the HI molecule in mixtures with nitrogen gas. Our data are compared with the previously published results for the fundamental bands of the HF and HCl molecules. It is shown that the line shifts are dominated by the vibrational dependence of the isotropic part of the intermolecular interaction potential.     

Algebraic expressions for vibration-rotation line intensities of near prolate asymmetric molecules: Application to SO2 molecule

A treatment of the intensities of vibration-rotation lines of near prolate asymmetric molecules is given, leading to explicit expressions relating the observed to the appropriate coefficients in the expansions of the potential energy and the dipole moment. The theoretical results are compared with experimental determinations of line intensities in the υ₁-band of sulfur dioxide.     

Fourth-order contributions to the rotational-vibrational matrix elements for diatomic molecules; application to the Fς′v(m) functions for CO

Using the rotational potential function expanded through the quartic term as a perturbation, and considering successively a quartic and a quintic dipole moment function, general expressions are obtained for the vibration-rotation matrix elements corresponding to the transitions vJ→?′J′ with ?′?v+5.The vibration-rotation interaction functions F^?′_v(m) are deduced for the transitions v→?′ (v=0, 10, 20 and?′?v+4) of CO from calculations including third then fourth-order contributions to the matrix elements. The results obtained for the coefficients of the quartic polynomials fitting these functions are compared and their validity is discussed.     

Theory of pressure-induced vibrational and rotational absorption of diatomic molecules at high temperatures

A derivation is given for the integrated absorption coefficient of pressure-induced pure rotational and vibrational transitions in binary collisions of homonuclear diatomic molecules of the same chemical species. The previously neglected effects of excited vibrational states, mechanical anharmonicity, and vibration-rotation interaction are taken into account to obtain more accurate absorption coefficients at high temperatures. In the region of the fundamental wave number the excited vibrational states make more of a contribution to the absorption than their relative population would lead one to expect.     

Influence of line interference on the vibration-rotation band shapes

The shapes of the CO, v₃, CO₂, and v₃ N₂O fundamental vibration-rotation bands have been studied at various temperatures and in the presence of several perturbing gases. Also the half-widths of CO vibration-rotation lines have been measured at 78 K. In the region of line wings, the measured absorption coefficients deviate from those given by the superposition of Lorentzian profiles. These deviations are explained by the collision-induced line interference that causes redistribution of absorption inside the band. A theory of line mixing is formulated which is based on Markov approximation and on the strong collision model. Simple analytical expressions are obtained for the band shape. The computed shapes are in satisfactory agreement with the experimental results. The deviations from the Lorentz absorption observed in pure CO and in CO-N₂ at low temperature are partially ascribed to the formation of van der Waals dimers.     

Pressure broadening of ammonia lines in the 6475åband at room and low temperatures

Measurements of pressure broadened half-widths have been performed for four ammonia vibration-rotation lines in the 6475Åband. Self-, hydrogen- and helium-broadening have been measured over a temperature range of 175–295 K. Pressure broadening coefficients and temperature dependence indices have been obtained for each line and broadening gas. A rotational quantum number dependence for the line width has been observed for all broadening gases studied.     

Theoretical study of the rovibrational dependence of nuclear hyperfine interactions in the v 3 band of SF6

The dependence of the spin-rotation hyperfine interaction on the vibration-rotation molecular state detected in the analysis of the hyperfine structures of the v ₃ band of SF₆ can be taken into account by introducing some of the formal operators given by Michelot. We have established the relationships between the coefficients of Michelot's formal operators and the molecular constants. This has enabled us to understand how far the formal coefficients are independent and to check the order of magnitude of spectral effects due to other hyperfine operators described by Michelot.     

Vibration-rotation bands of hydrogen halides dissolved in liquefied noble gases

Fundamental absorption bands of hydrogen halides have been studied in dilute solutions in liquefied Ar, Kr, and Xe. The second band moments obtained from experimental profiles are in agreement with the theoretical values for vibration-rotation bands. Extensive rotational structure of the HCl and HF bands has been recorded in Kr and Xe solutions. The observed rotational lineshifts and linewidths are compared with the available gas phase data.     

Theory of pressure-induced vibrational and rotational absorption of diatomic molecules colliding with atoms at high temperatures

A derivation is given for the integrated absorption coefficient of pressure-induced pure rotational and vibrational transitions in binary collisions of homonuclear diatomic molecules with neutral atoms. The previously neglected effects of excited vibrational states, mechanical anharmonicity, vibration-rotation interaction, transverse components of the dipole moment, and a higher order term in the expansion of the z component of the dipole moment are taken into account to obtain more accurate absorption coefficients at temperatures above 423 K. In the region of the fundamental wave number the excited vibrational states make more of a contribution to the absorption than their relative populations would indicate.     

Temperature dependence of rare gas broadening and shifting of first harmonic lines of H35Cl

Widths and shifts of HCl vibration-rotation lines, pressurized by rare gases, have been measured for the 0–2 band as functions of temperature. The results reported here complement previously published results on the fundamental band. The model of Smith, Giraud and Cooper is used to calculate widths and shifts; good agreement is obtained between experiment and theory. Problems concerning the accuracy of available potential energy surfaces and the calculation of differential cross sections are discussed briefly.     

Exact vibration-rotation kinetic energy operators in two sets of valence coordinates for centrally connected penta-atomic molecules

The exact vibration-rotation quantum mechanical kinetic energy operator (KEO) for centrally-connected penta-atomic molecules such as methane and its isotopomers is derived for two sets of internal valence coordinates: the polyspherical coordinates and the bond-angle valence coordinates. The vibrational KEO including the pseudo-potential term is discussed for two forms of the modified Jacobian. For the rotational and vibration-rotation coupling KEO, results for two schemes of embedding the body-fixed coordinate system are presented: the bond embedding and the bisector embedding. Full expressions for the bisector embedding are too complicated to give in detail, but the working connection between the two embedding schemes is given. The future applications, including the perturbative and variational calculation of the vibrations and/or rotations for centrally connected penta-atomic molecules using the vibration-rotation KEO expressions derived in this work, are discussed.     

Absorption intensities for vibration-rotation bands and the dipole-moment expansion of HBr

Line intensities in the four 0–2, 0–3, 0–4, 0–5 vibration-rotation bands of HBr were measured. The electric dipole matrix elements 〈0|M|ν'〉 for vibrational transitions with ν'?5 have been calculated by using a Dunham potential and the analytical solution of the Schrödinger equation described by R.H. Tipping. A dipole-moment expansion accurate to M₅ was determined by fitting these matrix elements to the available experimental data on line intensities. The experimental results were also used to calculate the Einstein coefficients of the R₀ lines for the bands ν' → ν′' with ? ν' ? 5.     

Classical treatment of vibration-rotation intensities for the Morse oscillator

The effect of vibration-rotation interaction on spectral line intensities is treated classically for the Morse oscillator. To describe the distribution of intensity in the R and P branches, one must take into account both the vibrational (radial) and the rotational (perpendicular) dipole moment functions. When this is done, the leading terms for the Fourier coefficients of these functions, as well as the Herman-Wallis factors, agree exactly with the corresponding quantum mechanical matrix elements in the Dunham limit.     

Infrared spectral line parameters of HBr and DBr at elevated temperatures

The electric dipole matrix elements <v'J'μvJ> for pure rotation and vibration-rotation transitions, with |;m|;<-40 and v<-v'<-6, have been derived for HBr and DBR by using the Rydberg-Klein-Rees (RKR) potentials and numerical solutions of the Schrödinger equation. An improved dipole-moment expansion was determined by fitting these matrix elements to the available experimental data on line intensities. A least squares analysis of the available line position constants gave an improved set of Dunham coefficients good for spectral lines with both large and small quantum numbers v and J. The results were then used to generate a compilation of individual line parameters for the Δv = 1 bands of HBr and DBr at temperatures up to 3000K. These parameters, together with previously compiled line parameters for HCl, HF, CO and NO, are being used for line-by-line calculations of radiance from a hot source as seen through an atmospheric path.