CO Fundamental Band Research Articles

Departures from LTE in the fundamental bands of CO in cool stars

Departures from LTE in the fundamental bands of CO in cool stars

Cw high-resolution car spectroscopy of H 2, D 2, and CH 4

Lines of the CO fundamental band are studied at low concentration in He, Ne, Ar, Xe or N2 as buffer gas from 10 to 600 torr. The coefficient β0 associated with the Dicke narrowing effect is determined for each of the five mixtures. To obtain the proper value of this coefficient, when the pressure increases, the absorber speed dependence of the pressure broadening γ0 must be taken into account. Pressure shifts are also measured, and a faint asymmetry is observed for the COXe mixture. The line scanning is done with a TDL tightly controlled by a Michelson interferometer. A precision better than one-thousandth for absorbed intensity and a wavenumber precision of a few 10−5 is reached. These precisions were found necessary for the needed parameter measurements.

The fundamental bands of CO as chromospheric indicators in late-type giant stars

Synthetic spectra are presented for the vibrational-rotational fundamental transitions (XV=1) in the ground electronic state of CO for the upper-photosphere--lower-chromosphere atmospheric model of Arcturus derived by Aryes. It is found that the CO spectrum is formed in LTE and the strongest molecular lines exhibit emission cores reflecting the chromospheric temperature rise. The CO fundamental bands offer an excellent observational probe for the presence of stellar chromospheres and a consistency check for chromospheric models derived from traditional chromospheric indicators. (AIP)

Measurement of line intensities of linear molecules under low resolution

By using the relation k v ⋍ S J /δ J applicable at sufficiently high pressures, at which the rotational fine structure in a band is smeared out completely, line intensities S J may be determined from measured spectral absorption coefficients and known local line spacings δ J . First, the validity of the approximation is ascertained by comparing the spectral absorption coefficient data of Penner and Weber and of Varanasi and Penner for the fundamental bands of CO and NO, respectively, with S J /δ J derived from the high resolution measurements of Benedict et al. (for CO) and of Abels and Shaw (for NO). Line intensity data obtained using this method are in good agreement with the high-resolution measurements of Toth (grating spectroscopy) for some unblended lines in the 00°0−02°1 band of N 2O and of Lacome et al. (laser- spectroscopy) for lines in the 10°0−00°1 band of N 2O.

Notizen: Investigations on the C2H2-O2 Chemical Laser

Side light investigations of the flame in the laser cavity resulting from the oxidation of acetylene showed the presence of H2O in this system. Stimulated emission in the fundamental band of CO is partially absorbed by the water formed in the reaction. This explains the very low total output of the C2H2-O2 chemical laser.

Method for Measuring Relative Transition Probabilities of Cascading Molecular Bands: Application to CO Fundamental Bands

A general method is presented to determine the relative transition probabilities for two molecular bands which have one vibrational level in common. It is based on optical gain (or loss) measurements on a number of vibration-rotation transitions in each of the two bands. The method has been applied to CO fundamental bands in the ground electronic state to yield |Rνν +1|2/|Rν −1ν|2 for v=6 through v=11, where Rν−1ν is the rotationless matrix element of the dipole moment connecting the v−1th and vth vibrational levels. The results were fitted by using the wavefunction approximation for Rν−1ν, and the ratio R04/R01=0.00021 was obtained.

Shock Tube Vibrational Relaxation Measurements: N2 Relaxation by H2O and the CO–N2 V–V Rate

Shock tube measurements of the rates of vibrational relaxation of N2 by H2O and the vibrational exchange between N2 and CO are described. Simultaneous measurements of H2O v2 ν2 band and CO fundamental band ir emission were performed in mixtures of 1%–10% CO+∼1% H2O+N2. Measurement of H2O emission by a calibrated optical system allowed an accurate determination of the concentration of H2O for each run. The CO emission had two, almost decoupled, regions of behavior which allowed determination of two relaxation times: Pτ NCe≈ 1.6 atm· μsec (V–V exchange relaxation time between N2 and CO) and Pτ NH≈ 1.5 atm· μsec (T–V relaxation of N2 by H2O), both for 960 〈T〈2200°K.

Intermolecular Potentials and Infrared Spectra

In an effort to learn more about the angle dependence of intermolecular potentials, pressure broadened infrared spectra have been compared with calculations from a trial potential. Infrared spectra of the CO fundamental absorption band were measured at densities of helium gas perturber from 10 to 100 amagats at room temperature. The same spectra were calculated from the potential using a semiclassical impact theory of overlapping lines. The comparisons show that the potential accounts quite well for the spectra except at low pressures, suggesting that the long-range part of the potential was too strong. Satisfactory agreement was obtained even at pressures which were so high that the impact theory is not rigorously applicable. The success of these calculations should encourage the use of this technique for, on the one hand, testing intermolecular potentials and, on the other, predicting pressure broadened spectra of molecular gases over a wide range of pressures.

Infrared Sidelight Studies in the High-Power Carbon Monoxide Laser

Spontaneous radiation on the CO fundamental vibration-rotation bands, created by sidelight emission from a liquid-nitrogen—cooled CO–He laser, has been studied spectroscopically. The CO rotational temperature and the relative populations of vibrational states v=1 to v=14 have been inferred. The vibrational population distribution is significantly non-Boltzmann.

Spectral and integrated intensity of CO fundamental band at elevated temperatures

The spectral absorption coefficient of CO fundamental band at temperatures from 300 to 1500°K is determined from the existing spectral absorption data in the strong-line approximation region and in the transition region. This has been achieved by use of the Godson approximation for the Elsasser function and the estimated mean values for the line half-width-spacing ratio at various temperatures. The resulting spectral absorption coefficients compare favorably with the available experimental data at room temperature and with the theoretical results at various temperatures. For the integrated intensity of the CO fundamental band extrapolated to STP the present investigation results in a value of 290 ± 16 aim −1 cm −2, which again is in good agreement with the recent experimental data of Breeze and Ferriso.

Integrated Intensity Measurements on the Fundamental and First Overtone Band Systems of CO Between 2500° and 5000°K

Measurements have been made of the total absolute integrated intensities of the 4.7-μ fundamental and 2.4-μ first overtone band systems of CO at various temperatures within the range 2500° to 5000°K. The CO gas sample was studied in emission using a reflected shock wave to raise the sample to the high temperatures. Effects of vibrational relaxation, dissociation, and shock structure have been considered in the data interpretation. Within the temperature range used in the present experiments, the integrated intensity of the CO fundamental band system remains constant. However, the integrated intensity of the CO first overtone band system shows a small increase with increasing temperature. The temperature dependencies of the two band systems are in agreement with the theoretical temperature dependencies. The present experimental results for CO extrapolated to STP are 289±29 and 2.3±0.3 cm−2·atm−1 for the total integrated band intensities of the fundamental and first overtone band systems, respectively.

Highly Precise Wavelengths in the Infrared II HCN, N_2O, and CO†

A discussion is given of the effect of mechanical errors in a grating drive on the accuracy with which line frequencies can be measured. It is shown that it is highly improbable that a mechanical device used to rotate a diffraction grating can be constructed with sufficient precision so that the line-frequency error will be determined by the optical information observable in the near infrared spectrum. By making use of the echelle spectrograph 67 lines of the 001–000 absorption band of HCN have been measured. Almost 400 lines from five N2O absorption bands arising from the ground state of the molecule have been measured. In addition, 11 lines from the 1–0 fundamental band of CO have been measured in order to determine ν0 for this band. In all cases only band lines have been measured which appear to be free of blends. The molecular constants of the above bands have been determined by making use of the combination relationships applying least-squares methods to the data. The line frequencies have then been calculated to four decimal places and presented in tables. The tables contain over 600 line frequencies. We believe the calculated line frequencies (lines free of blends) have an absolute accuracy of about 1 part in 5×106 and a relative accuracy referring to lines within a given band somewhat greater.