Intensities Of Hot Bands Research Articles

Analysis of Reliability of Spectral Water Vapor Line Parameters at High Temperatures in Spectroscopic Databases

Parameters of high-temperature water vapor spectral lines presented in the well-known spectroscopic databases are discussed. As a reliability criterion for parameter values, recent experimental data on the transmittance measured with spectral resolution of 1 cm–1 at Т ~ 1000 K are employed. As a result of our analysis, 156 spectral lines were revealed (12 of them were found previously) in the HITEMP2010 database the use of which in calculations of the transmittance leads to considerable deviations (≥20%) from the available experimental data. The line intensities determined by this method exceed by 3 times and more the data presented in other spectroscopic bases. Additionally, the line intensities from the HITEMP2010 database in the spectral range 10–6000 cm–1 are completely compared with the result of semiempirical calculation at the high temperature available from the literature. The hot bands for which the relative deviation of the integral intensities exceeds 10% at T = 1302 K are identified. It is established that as a whole, the most reliable integral hot band intensities are contained in the HITEMP2010 database. This is confirmed by their least deviations from the measured transmittance at high temperatures. As a result, it is demonstrated that to obtain the best coincidence (Δav = 2.64%) with the measured data in the range 1000–2000 cm–1 in calculation based on the HITEMP2010 database, the parameter values recommended in the present work for lines with overestimated intensities and different distribution of the temperature coefficients must be used.

Efficient and automatic calculation of optical band shapes and resonance Raman spectra for larger molecules within the independent mode displaced harmonic oscillator model

In this work, an improved method for the efficient automatic simulation of optical band shapes and resonance Raman (rR) intensities within the "independent mode displaced harmonic oscillator" is described. Despite the relative simplicity of this model, it is able to account for the intensity distribution in absorption (ABS), fluorescence, and rR spectra corresponding to strongly dipole allowed electronic transitions with high accuracy. In order to include temperature-induced effects, we propose a simple extension of the time dependent wavepacket formalism developed by Heller which enables one to derive analytical expressions for the intensities of hot bands in ABS and rR spectra from the dependence of the wavepacket evolution on its initial coordinate. We have also greatly optimized the computational procedures for numerical integration of complicated oscillating integrals. This is important for efficient simulations of higher-order rR spectra and excitation profiles, as well as for the fitting of experimental spectra of large molecules. In particular, the multimode damping mechanism is taken into account for efficient reduction of the upper time limit in the numerical integration. Excited state energy gradient as well as excited state geometry optimization calculations are employed in order to determine excited state dimensionless normal coordinate displacements. The gradient techniques are highly cost-effective provided that analytical excited state derivatives with respect to nuclear displacements are available. Through comparison with experimental spectra of some representative molecules, we illustrate that the gradient techniques can even outperform the geometry optimization method if the harmonic approximation becomes inadequate.

First observation of the 3ν1+2ν3−ν3 band of 16O3: problem of consistency between cold and hot band intensities

The 3ν1+2ν3 − ν3 band of 16O3 has been observed for the first time below the residual of all the known absorbing bands in the 4100 cm−1 region. The rovibrational transitions have been assigned for J and K a up to 31 and 11, respectively, leading to a root-mean-square (RMS) deviation of 2.3 × 10−3 cm−1. The observed line intensities are reproduced with a RMS deviation of 10%, which is very satisfactory bearing in mind the weakness of this band. The problem of consistency of the intensity of the cold-to-hot band extrapolation and of the effects of anharmonic resonances with distant partners on transition moment parameters is discussed. This work clearly shows the necessity to account for strong anharmonic coupling between distant vibrational states in order to be theoretically consistent.

Assignments and Intensities of 14NH3 Hot Bands in the 5- to 8-μm (3ν2−ν2, ν2+ν4−ν2) and 4-μm (4ν2−ν2, ν1−ν2, ν3−ν2 and 2ν4−ν2) Regions

To complete the analysis of the complex infrared spectra of 14NH3 in the 4- to 8-μm region, we assigned nearly 1200 transitions in the 3ν2−ν2, ν2+ν4−ν2, ν1−ν2, ν3−ν2, 2ν4−ν2 and 4ν2−ν2 hot bands using the upper state energy levels determined by our previous studies at 4 and 3 μm (J. Mol. Spectrosc.173, 120–145 (1995); 193, 46–71 (1999)). Line intensities of those hot bands were analyzed using measurements retrieved from 0.0056 and 0.011 cm−1 unapodized resolution FT spectra recorded at Kitt Peak National Observatory. By a least-squares fit of vibrational-inversion transition moments, over 770 intensity measurements are modeled to ±7.2% and ±8.9% in the 5- to 8-μm and 4-μm regions, respectively. The values of the transition dipole moment were determined to obtain the band strengths of hot bands. In the 5- to 8-μm region, the band strengths in cm−2 atm−1 at 296 K of 3ν2−ν2 (a←s), 3ν2−ν2 (s←a), ν2+ν4−ν2 (s←s) and ν2+ν4−ν2 (a←a) were found to be 0.000075(23), 0.351(22), 0.689(32), and 0.525(44), respectively. In the 4-μm region, for the ν3−ν2 (s←s), ν3−ν2 (a←a), 2ν4l4=±2−ν2 (s←s), and ν4l4=±2−ν2 (a←a), they were estimated to be 0.0703(32), 0.0599(27), 0.00547(34), and 0.00473(29), respectively at 296 K. Also, about 100 line intensities of the ν1−ν2 (a←s), ν1−ν2 (s←a), 2ν4l4=0−ν2 (a←s), 2ν4l4=0−ν2 (s←a), and 4ν2−ν2 (s←a) weak hot bands were measured and reported. The prediction generated by the present study is available for the detection of 14NH3 in exoplanet atmospheres and brown dwarf stars with relatively high temperature (∼1000 K). A few self-broadened linewidths are reported to demonstrate that there is a large variation with the vibrational quanta.

Line intensities of hot bands in the [formula omitted] spectral region of acetylene 12C 2H 2

Using FTS spectra (apodized FWHM: 0.0014 cm −1 ), absolute intensities have been measured for 355 hot lines of 12C 2H 2 in the 13.6 μm spectral region, with an accuracy of ±5%. Intensities of lines with J values up to 31 have been obtained for the five following hot bands: 2 ν 5 0− ν 5 1, 2 ν 5 2− ν 5 1, ( ν 4+ ν 5) + 0− ν 4 1, ( ν 4+ ν 5) − 0− ν 4 1, and ( ν 4+ ν 5) 2− ν 4 1. The vibrational transition dipole moment squared and the Herman–Wallis coefficients have been determined for each band. On the whole, the measured line intensities have been found greater than the 1996 HITRAN values by about 11%.

The High Resolution Infrared Spectrum of CH3D in the Region 900–1700 cm−1

The high resolution absorption spectrum of CH3D in the region 900–1700 cm−1has been reexamined on the basis of new long path experimental data recorded with the Fourier transform spectrometer at Kitt Peak. A theoretical model used previously for spherical rotors has been adapted for symmetric top molecules in order to analyze the vibrational polyads of CH3D simultaneously. Both triad and nonad–triad band systems have been investigated. The hot band intensities were estimated through direct extrapolation of the triad dipole moments. Six hundred lines from the hot bands have been assigned and combined with other data for the triad. The main hot bands contributions are due to 2ν6− ν6, 2ν3− ν3, ν3+ ν6− ν3and ν3+ ν6− ν6bands. The standard deviation achieved for 3377 line positions of the triad was 0.56 10−3cm−1, representing an improvement of one order of magnitude with respect to the most recent analysis.

Intensities of Hot-Band Transitions: HCN Hot Bands

A simple vibrational Hönl-London-type formula for hot-band intensities is tested by measuring the intensities of a number of vibrational transitions, including many hot bands, for HCN. This vibrational intensity formula is based on one- and two-dimensional harmonic oscillator functions and a nonlinear electric dipole function that is expanded in a Taylor series with respect to the normal coordinates. It is shown that, when this formula is included, the observed transition dipoles for the bending hot bands differ by only a few percent from the transition dipoles for the same quantum number changes from the ground state. Infrared absorption intensity measurements are given for the transition dipoles for the transitions 01 10-0000, 0200-0000, 0310-0000, 0400-0000, 1000-0110, 1200-0000, and 2000-0000 and the accompanying hot bands involving the lower states ν2 = 1, 2, and 3. This simple model is limited to well-behaved systems, but would be useful for estimating the intensities of some high-temperature spectra. For HCN the Herman-Wallis constants that are quadratic in J(or m) are shown to be determined principally by the effect of l-type resonance.

Metastable decay of N +2He n (υ = 1) (1 < n⩽6) clusters

Laser and mass spectroscopic techniques have been combined to explore the fragmentation process of metastable N + 2He n ionic clusters. It has been found that clusters possessing a single quantum of the N⋯N stretching vibration decay on the 100 μm time scale. The rate for the relaxation of the N⋯N stretching vibration in larger N + 2He n complexes has been determined by measuring the relative intensities of hot bands involving the N⋯N stretch vibration in the B ← X spectra and comparing with the hot-band intensity for the N + 2He complex for which a lifetime for the υ = 1 state of 220 ± 30 μm has been previously measured. While for the smaller complexes ( n = 1–3) the relaxation rate is proportional to ligand number there appears to be some saturation for the larger species ( n = 4–6). The roughly linear increase in dissociation rate with ligand number and the ionic fragment size distribution are consistent with a two-step fragmentation process whereby a single He atom collides inelastically with the vibrationally excited core with the recoiling N + 2 undergoing intracluster collisions with the other ligands leading to further He evaporations.

The B2Σ+ ← X2Σ+ Transition of HgI

The B2Σ+ ← X2Σ+ fluorescence excitation spectrum of HgI between 367 and 322 nm is presented. The radicals were produced and rotationally cooled in a corona-excited supersonic expansion. Spectral analysis of the isotopomer fine structure has shown that transitions from the lowest ground state levels excite a wide range of high vibrational levels in the B ion-pair potential. (vB = 30-70). Excited state molecular constants are reported which are valid between vB = 0 and 70. A new B-state equilibrium bondlength has been obtained from Franck-Condon calculations which reproduce the hot-band intensities in the excitation spectra. New Franek-Condon factors were derived for 25 ≥ vB ≥ 0 and 20 ≥ vX ≥ 0 which are expected to be of use in the interpretation of the HgI B → X laser output near 440 nm.

Rotationally resolved laser-induced fluorescence excitation studies of CH 3O

The laser-induced fluorescence (LIF) excitation spectrum of the A 2A 1 ← X 2E band system of the CH 3O radical has been studied at both low (≈ 10 cm −1) and high (≈ 0.1 cm −1) resolution. CH 3O radicals were generated in a discharge flow system via the reaction F + CH 3OH → CH 3O + HF. Low-resolution excitation spectra were dominated by a progression 3 0 n in the upper state CO stretch vibration ν′ 3 in agreement with earlier findings reported in the literature. The previously questioned vibrational band assignment was ascertained by comparing fundamental and hot band intensities as a function of temperature. Rotationally resolved excitation scans were performed for the 0 0 0 band. A 50 cm −1 wide portion towards the less congested blue side of this band was rotationally assigned. A least-squares fit to the observed line positions yielded precise values of the A-state electronic origin and the rotational constants. After removal of the X -state spin-orbit splitting the value for the origin is T 0 = 31613.9 ± 0.5 cm −1.

Infrared absorption by gas mixtures in the 300–850 K temperature range I—4.3 μm and 2.7 μm CO 2 spectra

Spectra have been measured with 1% accuracy in a vacuum-tight cell in the 0.2-1 atm pressure range. They are compared with a line-by-line calculation using Rothman's data on line-positions and band-strengths, a T -0.8 dependence of line-widths γ, and recent values for γ s co 2-co 2 and γ s co 2-N 2 at STP. The calculations agree with CO 2 and CO 2-N 2 spectra in the 4.3 μm band, except between 2200 and 2300 cm -1; hot-band intensities are overestimated. The same conclusion holds for CO 2-H 2O mixtures for the mean value ḡg s CO 2-H 2O = 0.11 cm -1. Calculations also agree with 2.7 μm-band spectra for intensities that are 20% lower than Rothman's.

Theoretical Herman-Wallis coefficients for C70 and D70 and the dipole-moment function of HCl

Theoretical expressions for the Herman-Wallis coefficients C 7 0 and D 7 0 and a correction term of order 2 B e /ω e times the leading term for C 6 0 have been derived in terms of the Dunham potential-energy parameters and series dipole-moment expansion coefficients by the method of computer algebra. After reviewing previous work on the extraction of the dipole-moment function for HCl from experimental data, the present results are applied to a determination of the series representation up to seventh order in the reduced displacement from the equilibrium internuclear separation. Coefficients for an alternate representation in terms of a Padé approximant are also obtained; this model dipole-moment function should enable one to estimate more accurately the higher overtone and highly excited hot-band intensities since it circumvents the divergence difficulties of the series expansion and has the correct asymptotic behavior at both small and large internuclear separations.

Intensities of hot bands in the dimol emissions of singlet molecular oxygen, O2(1? g )

The temperature dependence of the three dimol emissions of oxygen O2(1Δg) at 579, 634 and 703 nm has been studied between 295 and 1500 K with a discharge-flow–shock-tube apparatus. The intensity increases with temperature and concentration as expected for these bimolecular processes, but there is a further increase which is attributed to the appearance of overlapping hot-band emissions from vibrationally excited molecules of O2(1Δg). For the 703 nm emission there is an additional contribution from hot bands of O2(1Σ+g).The relative emissivities of the bands and the rate constants for the collisional emission reactions have been determined and are presented in table 4.The values found appear to indicate that, for these simultaneous transitions from two colliding molecules, the intensities are governed by an electronic transition probability which changes rapidly with intermolecular distance.

Cis and trans methyl nitrite: Gas phase i.r. spectra, band envelope analysis, hot band progressions and assignments

The gas phase vibrational spectrum of methyl nitrite has been recorded over the range 4000-300 cm −1. All the fundamental modes of both the cis and trans conformers have been assigned. The complex rotational band envelopes arising from overlap of different vibrational transitions of the two conformers have been simulated as superpositions of intensity weighted vibration—rotation bands. The simulation process allowed estimates for relative magnitudes of different components of transition moments contributing to these band intensities. For the cis conformer, hot band progressions arising from the methyl and NO torsions have been identified for a number of fundamental modes. The simulation of the complete band contour in such cases yields information about Boltzmann factors for the torsional excited states from which reliable estimates of the torsional frequencies are obtained. The hot bands also provide accurate information about anharmonicity constants. For the trans conformer hot band progressions were found to be too complex because of nearly free internal rotations of the methyl group. A large number of combination modes have also been assigned. These assignnents yield estimates for the two torsional modes of the cis conformer which are in agreement with those obtained from relative intensities of hot bands. An estimate of the NO torsional frequency of the trans species has also been obtained from the combination modes.

The Analysis of the Molecular Vibration by the Molecular Orbital Method. I. Application to HCN

Abstract The approximate self-consistent molecular orbital method has been applied to the analysis of the vibrational spectrum of HCN. The frequencies of the fundamental, overtone, and combination bands in the region from about 700 to 12000 cm−1 have been calculated, and their absolute infrared absorption intensities have been estimated, the variational method being used in this calculation. Also, the frequencies and absorption intensities of hot bands, referring to the bending vibration, have been calculated. In comparison with the experimental results, the calculated frequencies were not always appropriate. However, it was found that these results are effective in the analysis of the molecular vibration if the calculated frequencies are discussed along with their infrared absorption intensities.