C. Chackerian

Vibration-rotational and rotational intensities for CO isotopes

Abstract Dipole moment matrix elements have been computed for the five most abundant isotopes of CO. The wave functions utilized were obtained from a direct solution of the Schrodinger equation with an accurate RKR potential. The dipole moment function, in the form of a Pade approximant, was chosen to reproduce the experimental measurements near equilibrium, to have the proper united and separated atom limits, and to have the correct long-range asymptotic functional dependence on internuclear separation. Because of the large number of transitions involved, and to facilitate applications, the squares of the dipole moment matrix elements were fitted by a least-squares procedure to polynomials in v and J. Predictions for the 5-0 and 6-0 rotationless matrix elements and Herman-Wallis coefficients are given, and their dependence on the isotopic reduced mass is discussed. For the pure rotational band, v = v ′ = 0, explicit Einstein A values and transition frequencies were calculated for the three most abundant isotopes for J up to 55. The corresponding dipole moment matrix elements were also fitted to simple polynomials in m and the dependence of the coefficients on the reduced mass given. The present results incorporate the most accurate and extensive intensity measurements and theoretical dipole moment function data for any heteronuclear diatomic molecule. In view of this, because of the importance of the CO laser, the accuracy of the spectral frequencies, and the ubiquity of the CO molecule, it is reasonable to expect that some of these lines, in particular, in the fundamental band of 12 C 16 O, can serve as laboratory standards for intensity measurements.

Updated line parameters for OH X2II–X2II (ν′',ν′) Transitions

Abstract New spectral line parameters have been generated for the OH X 2 II–X 2 II transitions for Δv = 0.., 6, with v ′ = 0.., 10, and J max = 49.5. HITRAN type line parameter sets with low intensity cutoffs are provided at 296 and 6000 K. Recent improvements in line intensities and line positions have been incorporated into the calculations.

Electric dipole moment function of the X 1Σ+ state of CO: Vibration–rotation matrix elements for transitions of gas laser and astrophysical interest

The electric dipole moment function of the ground electronic state of carbon monoxide has been determined by combining numerical solutions of the radial Schrodinger equation with absolute intensity data of vibration–rotation bands. The derived dipole moment function is used to calculate matrix elements of interest to stellar astronomy and of importance in the carbon monoxide laser.

Infrared measurements of the ClO radical

Abstract High-resolution infrared spectra of the fundamental (v = 1–0) and first overtone (v = 2–0) bands of the ClO ( X 2 Π 3 2 , 2 Π 1 2 ) radical have been observed using a Fourier transform spectrometer and a diode laser. Frequencies and relative absorption line intensities have been measured and analyzed. An improved set of rovibrational constants for both 35ClO and 37ClO and a table of line positions and intensities are given. Relative intensity measurements are used to determine the rotational dependence of the intensities, and thereby determine the Herman-Wallis effect. An integrated band intensity of 11.3 ± 2.0 cm−2 atm−1 is determined for v = 1–0 from the first Herman-Wallis constant in a manner independent of any concentration determination.

Linewidths and transition probabilities for the carbon monoxide laser lines

The pressure broadening at high temperatures and the radiative transition probabilities for some of the carbon monoxide vibration‐rotation transitions, Δν = 1, have been measured by the absorption of laser light in shock heated CO. The results are compared with other experimental data, and formulas for pressure broadening and the dipole moment function of CO are deduced.

Anhydrous nitric acid integrated absorption cross sections: 820–5300 cm−1

Abstract Fourier transform infrared absorbance measurements of small aliquots of anhydrous nitric acid were used to determine regional, integrated cross sections at 278.2, 298.22 and 323.15 K . Spectra were recorded with pressure broadened samples (1 atmosphere nitrogen), in a 20 cm path length cell at a spectral resolution of 0.112 cm −1 . Spectral regions measured include the vibrational bands: ν 1 (∼3552 cm −1 ) , ν 2 (∼1710 cm −1 ) , ν3, ν 4 (∼1320 cm −1 ) , and ν5, 2ν 9 (∼890 cm −1 ) and regions of weaker absorption between 820 and 5300 cm −1 . We observe expected changes in the distribution of rovibrational intensities with temperature, but to the accuracy of our measurements, cross-sections integrated over entire vibrational bands are independent of temperature.

Prognosis for a mid-infrared magnetic rotation spectrometer for the in situ detection of atmospheric free radicals

Mid-infrared magnetic rotation spectroscopy (MRS) experiments on nitric oxide (NO) are quantitatively modeled by theoretical calculations. The verified theory is used to specify an instrument that can make in situ measurements on NO and NO(2) in the Earths atmosphere at a sensitivity level of a few parts in 10(12) by volume per second. The prototype instrument used in the experiments has an extrapolated detection limit for NO of 30 parts in 10(9) for a 1-s integration time over a 12-cm path length. The detection limit is an extrapolation of experimental results to a signal-to-noise ratio of one, where the noise is considered to be one-half the peak-to-peak baseline noise. Also discussed are the various factors that can limit the sensitivity of a MRS spectrometer that uses liquid-nitrogen-cooled lead-salt diode lasers and photovoltaic detectors.

CO 1-0 band isotopic lines as intensity standards

Abstract Fundamental band vibration-rotational line intensities are reported for the 12 C 16 O, 13 C 16 O, and 12 C 18 O molecules. The intensities were computed using numerically obtained matrix elements of a recently determined electric dipole moment function. We also report new intensity measurements for some of these lines obtained via high-resolution Fourier spectra. The overall consistency (≈2.2%) between our calculations, which are based on recent experimental determinations of CO 1-0 band intensities, not including our own, and our independent experimental results suggests that the lines of the fundamental band of CO can be used as absolute intensity standards.

Vibration-rotation intensities of SiO

Abstract Dipole moment matrix elements have been computed for a large number of transitions of astrophysical interest for the more abundant isotopes of SiO. The wave functions utilized were obtained from a direct solution of the Schrodinger equation with an accurate RKR potential. The dipole moment function, in the form of a Pade approximant, was chosen to reproduce the experimental measurements near equilibrium, to have the proper united and separated atom limits, and to have the correct long-range asymptotic dependence on internuclear separation. Because of the large number of transitions involved, and to facilitate applications, the squares of the dipole moment matrix elements were fitted by a least-squares procedure to polynomials in v and J. In addition, Einstein A coefficients are given for observed maser transitions and for selected vibrational bands. These latter are compared with previous calculations, and it is concluded that for the higher Δv transitions, the present results represent a significant improvement.

Rovibrational intensities for the Δv=1 bands of the X 3Σ− NH radical: Experiment and theory

The vibrational transition dipole moment for the highly reactive radical species, NH, in its ground electronic state is obtained via the Herman–Wallis effect manifest in emission spectra produced in a plasma reactor. The results of these experiments on the five lowest Δv=1 bands, are in good agreement with high quality ab initio calculations of the electric dipole moment function.