Nitrogen-broadening Coefficients Research Articles

N2-broadening coefficients of CH3CN rovibrational lines and their temperature dependence for the Earth and Titan atmospheres

Theoretical nitrogen-broadening coefficients and their temperature exponents for methyl cyanide lines in parallel (ΔK=0) bands are calculated by a semi-empirical approach suitable for CH3X-type absorbers with large dipole moments. Together with the standard four-parameter correction factor determined from fitting on experimental line widths for each fixed K and requiring an extrapolation for higher K inaccessible experimentally, a new form accounting explicitly for the K-dependence and reducing the number of required parameters is proposed and successfully tested. Extensive (0⩽J⩽70, 0⩽K⩽20) R- and P-line lists are provided for the Earth and Titan atmosphere temperature ranges, which could be useful for atmospheric/astrophysical applications and spectroscopic databases.

An experimental and theoretical study of nitrogen-broadened acetylene lines

We present experimental nitrogen-broadening coefficients derived from Voigt profiles of isotropic Raman Q-lines measured in the ν2 band of acetylene (C2H2) at 150K and 298K, and compare them to theoretical values obtained through calculations that were carried out specifically for this work. Namely, full classical calculations based on Gordon׳s approach, two kinds of semi-classical calculations based on Robert–Bonamy method as well as full quantum dynamical calculations were performed. All the computations employed exactly the same ab initio potential energy surface for the C2H2–N2 system which is, to our knowledge, the most realistic, accurate and up-to-date one. The resulting calculated collisional half-widths are in good agreement with the experimental ones only for the full classical and quantum dynamical methods. In addition, we have performed similar calculations for IR absorption lines and compared the results to bibliographic values. Results obtained with the full classical method are again in good agreement with the available room temperature experimental data. The quantum dynamical close-coupling calculations are too time consuming to provide a complete set of values and therefore have been performed only for the R(0) line of C2H2. The broadening coefficient obtained for this line at 173K and 297K also compares quite well with the available experimental data. The traditional Robert–Bonamy semi-classical formalism, however, strongly overestimates the values of half-width for both Q- and R-lines. The refined semi-classical Robert–Bonamy method, first proposed for the calculations of pressure broadening coefficients of isotropic Raman lines, is also used for IR lines. By using this improved model that takes into account effects from line coupling, the calculated semi-classical widths are significantly reduced and closer to the measured ones.

Measurements of nitrogen-broadening coefficients in the ν3 band of the hydroperoxyl radical using a continuous wave quantum cascade laser

Abstract Mid-infrared absorption spectroscopy was applied to the detection of the hydroperoxyl radical (HO 2 ) in pulsed laser photolysis combined with a laser absorption kinetics reactor. The transition of the ν 3 vibrational band assigned to the O–O stretch mode around 1065 cm −1 was probed with a thermoelectrically cooled, continuous wave, mid-infrared, distributed feedback quantum cascade laser (QCL). The HO 2 was generated through 355 nm photolysis of Cl 2 /1,4- c -C 6 H 8 /O 2 mixtures. The mid-infrared absorption spectrum of the HO 2 radical was recorded between 1064 and 1065.5 cm −1 . The absorption line shapes were well represented by the Voigt profile. The nitrogen-broadening coefficients of the HO 2 radical at 295 K were determined for four absorption lines around 1065 cm −1 . Mid-infrared absorption detection using a QCL as a spectroscopic light source is a powerful method in spectroscopic and kinetics studies of the HO 2 radical.

Hydrogen and helium pressure broadening of water transitions in the 380– [formula omitted] region

We present results of recent experiments on the pressure broadening of pure rotational transitions of H 2 16O water in the 380– 600 cm −1 range by hydrogen and helium. The hydrogen coefficients vary between 0.033 and 0.076 cm −1/ atm (average: 0.056 cm −1/ atm) while the helium coefficients vary between 0.006 and 0.017 cm −1/ atm (average: 0.013 cm −1/ atm) . While this average hydrogen-broadening coefficient matches the average nitrogen-broadening coefficient we observed in this region earlier, the range over which they vary is narrower for hydrogen than for nitrogen. We find that previously published complex Robert–Bonamy formalism calculations of the hydrogen coefficients are broadly consistent with these results, and that, to some extent, our experimental results can be predicted from HITRAN air widths.

Nitrogen broadening and shift coefficients in the 4.2–4.5-μm bands of CO 2

In this study we report the first high-resolution measurements of pressure broadening and pressure-induced shift coefficients due to nitrogen for rovibrational transitions in the ν 3 band of 13 C 16 O 2 . N 2 broadening and shift coefficients of ν 3 12 C 16 O 2 transitions were also measured. In addition, nitrogen-broadening coefficients for many transitions in the ν 3+ ν 2− ν 2 hot band of 13 C 16 O 2 as well as the ν 3 band of 13 C 16 O 18 O were also determined. The results were obtained by analyzing five high-resolution ( 0.0028 cm −1 ) room temperature laboratory absorption spectra with a multispectrum nonlinear least-squares spectral fitting technique. The data were recorded with the McMath-Pierce Fourier transform spectrometer of the National Solar Observatory on Kitt Peak using a 4.08 cm sample cell, total pressures up to 470 Torr , and a 90% 13 C -enriched CO 2 sample. For the pressure-broadened spectra the 13 C 16 O 2 volume-mixing ratios were⩽0.5%. Similar to broadening coefficients, the measured pressure shift coefficients were also found to be transition dependent. However, the shift coefficients were different in the P and R branch lines with the same rotational quantum number, J. The measured nitrogen-broadening coefficients range from 0.0960 to 0.0643 cm −1 atm −1 at 296 K . The measured shift coefficients were all negative and varied between 0 and −0.0036 cm −1 atm −1 . The results obtained are compared with other values reported in the literature.

Multispectrum analysis of self- and nitrogen-broadening, pressure shifting and line mixing in the ν3 parallel band of 12CH 3D

Lorentz self- and nitrogen-broadening coefficients as well as self- and nitrogen-pressure induced shift coefficients were measured at room temperature for more than 440 transitions in the QP, QQ and QR branches of the ν 3( A1) parallel band of 12CH 3D. The simultaneous multispectrum nonlinear least-squares fitting analysis was performed in the 1140– 1440 cm −1 region using 14 spectra of room temperature gas recorded with the McMath–Pierce Fourier transform spectrometer ( 0.005 cm −1 unapodized resolution) of the National Solar Observatory (NSO) on Kitt Peak. The measured self-broadening coefficients varied from about 0.025 cm −1 atm −1 at 296 K for high J, K transitions to about 0.09 cm −1 atm −1 at 296 K for low J, K transitions. In the case of nitrogen broadening these values ranged from about 0.023 to 0.073 cm −1 atm −1 at 296 K . The majority (>90%) of the self-pressure induced shift coefficients as well as nitrogen-pressure-induced shift coefficients was negative with values varying between approximately 0 and −0.012 cm −1 atm −1 . However, similar to air-induced pressure-shift coefficients determined in an earlier study, the measured self- and nitrogen-induced pressure-shift coefficients were positive for the QR-branch transitions with J″= K″, varying from 0 to about +0.009 cm −1 atm −1 . Weak line mixing effects were observed in several high- J lines with K″=3 splitting and approximate values for the off-diagonal relaxation matrix-element coefficients were determined for a few A 1A 2 (A +A −) split components. Comparisons are made between the measured self- and nitrogen-broadening and shift coefficients, and the results are also compared with measurements in other bands.

Self- and nitrogen broadening of the ν1020 11,10←19 10,9 ethylene transition at [formula omitted

Self- and nitrogen (N 2) broadening of ethylene (C 2H 4) have been measured for the ν 10 20 11,10←19 10,9 ethylene transition at 927.01879 cm −1 . The measurements were made using infrared heterodyne spectroscopy with a spectral resolution of ∼1.7×10 −4cm −1. At 296 K , the retrieved self-broadening coefficient for the observed transition is 0.1244(92) cm −1/ atm ; the nitrogen-broadening coefficient is 0.0757(99) cm −1/ atm . These results represent the most conservative treatment of experimental and statistical errors. A different purely statistical approach provides consistent values with uncertainties of only a few percent.

Multispectrum analysis of self- and N 2-broadening, shifting and line mixing coefficients in the ν6 band of 12CH 3D

A multispectrum nonlinear least-squares fitting technique has been applied to determine accurate zero-pressure line center positions, Lorentz self- and N 2-broadening coefficients and self- and N 2-induced pressure shift coefficients of transitions in the ν 6 (E) perpendicular band of 12CH 3D between 1035 and 1270 cm −1 . Seventeen high-resolution (0.002– 0.006 cm −1 ) room temperature absorption spectra recorded with two Fourier transform spectrometers (FTS) were analyzed together. Self-broadening coefficients for over 700 transitions and self-shift coefficients for more than 600 transitions were determined. Measurements of nitrogen-broadening coefficients for more than 480 transitions and nitrogen pressure induced shift coefficients for nearly 430 transitions were also made. The measurements include transitions with rotational quantum numbers as high as J″=18 and K″=15 and several forbidden transitions. The measurements were made in all six sub-bands ( P P, P Q, P R, R P, R Q and RR). The measured self-broadening coefficients vary from 0.025– 0.096 cm −1 atm −1 at 296 K and the N 2-broadening coefficients from 0.02 to 0.08 cm −1 atm −1 at 296 K . Self-induced-shift coefficients range from −0.014 to +0.004 cm −1 atm −1 while the nitrogen-induced-shift coefficients vary from −0.013 to +0.008 cm −1 atm −1 . Very few of the measured pressure-shift coefficients were positive, and the positive shift coefficients were mostly associated with the J″= K″ transitions in the PQ sub-bands. The off-diagonal relaxation matrix element coefficients of a number of transitions with K″=3 doublets for both self- and N 2-broadening were also obtained. The results obtained with the two different broadening gases are compared and discussed. Comparisons with previous values from the literature are also made.

Intensity Measurements and Collision-Broadening Coefficients for the Oxygen A Band Measured by Intracavity Laser Absorption Spectroscopy

High-sensitivity, high-resolution intracavity laser absorption spectroscopy (ICLAS) has been used to measure line intensities, nitrogen-broadening coefficients, and self-broadening coefficients in the A band (b1Σ+g ← X3Σ−g) of oxygen. Both linear cavity and ring cavity ICLAS configurations were used for these measurements, and the results were intercompared. The results were compared to values measured using long-path multiple-reflection cells by K. D. Ritter and T. D. Wilkinson [J. Mol. Spectrosc. 121, 1–19 (1987)] and L. Brown and C. Plymate, [J. Mol. Spectrosc. 199, 166–179 (2000)]. New results are included for weakly absorbing transitions, not observed in the earlier measurements, such as high rotational states (up to J = 39), hot-band transitions (v′ = 1 ← v" = 1), and isotopically substituted species (18O2 and 16O18O). Isotopic variants (16O2, 18O2, and 16O18O) have similar broadening coefficients for corresponding rotational levels, but the self-broadening coefficients are larger in the hot band (v′ = v" = 1) as compared with v′ = v" = 0 transitions. An ECS-EP scaling analysis of the v′ = v" = 0 self-broadening data accurately represents the available data, with the exception of the N = 0 and N = 1 levels.

Nitrogen-broadening in the nitric oxide first overtone band

Measured room temperature nitrogen-broadening coefficients are given for about 60 Λ-doublets belonging to the allowed sub-bands of the first overtone of nitric oxide, between 3620 and 3790 cm −1. Whereas a slight differential broadening (3.2% on the average) is observed between the two sub-bands, no significant vibrational dependence appears when one compares these values with those available for the fundamental band. Combining the N 2-broadening coefficients with the O 2-broadening coefficients recently published, the air-broadening required for atmospheric applications appears to be lower than the N 2-broadening by 2%.

Diode laser spectroscopic measurement of line shape of (ν 1 +3ν 3 ) band transitions of acetylene

A near-infrared diode laser spectrometer is set up to study the absorption line shape of acetylene in the 782 nm region. The second-derivative spectra recorded by source modulation technique have enhanced sensitivity. Careful choice of operating current and diode temperature leads to distortion-free line shape for six rotational components of the (ν1+3ν3) overtone-combination mode of acetylene. Self- and nitrogen-broadening coefficients and line-strength parameters have been extracted by fitting the observed line shape with Voigt profiles. There is no evidence of the effect of velocity changing collisions on the line shape in this near-infrared band.

Line Shift Investigations for Different Isotopomers of Carbon Monoxide

Line shift coefficients for five lines of five different isotopomers in the fundamental band of CO in the spectral region near 2058 cm−1were measured using a three channel lead salt diode laser spectrometer. The study includes the linesP(3) of13C17O,R(3) of13C18O,P(9) of12C18O,P(10) of13C16O, andP(21) of12C16O, and covers collisions with N2, O2, H2, D2, He, Ne, Ar, Kr, and Xe. Line shifts of the isotopomers13C16O,12C18O,13C18O, and13C17O were determined for the first time. Within the experimental uncertainty no significant dependence of the shift effect on the isotopomer was found. TheR-branch line under study shows a smaller line shift coefficient than aP-branch line with a similar rotational quantum number. With increasing mass of the noble gas perturber the absolute size of the shift coefficient increases. Moreover self- and nitrogen-broadening coefficients for the isotopomer lines were determined. Compared to previous measurements no significant deviations between different isotopomers were observed.

Pressure-Broadening Investigation of NO2in the Near Infrared

In this paper we report the data for self-, oxygen-, and nitrogen-broadening coefficients for 6 NO2lines belonging to two different bands: the (0 3 0)–(0 0 0) vibrational transition of theÃ2B2←X̃2A1system at 8360 Å and the (2 13 1)–(0 0 0) vibrational transition within theX̃2A1electronic ground state at 7390 Å. These measurements were performed using a differential absorption spectrometer based on semiconductor diode lasers emitting in the near-infrared region. We also report wavelength measurements for 14 lines of the above-cited bands obtained by means of a Michelson wavemeter with an accuracy of one part in 107.

Simultaneous detection of CO and CO 2 using a semiconductor DFB diode laser at 1.578 μm

and CO at a wavelength of λ=1578 nm. Sensitivity measurements under different conditions have been performed and the detection limit of the apparatus was measured to be less than 10 mTorr over a 1-m path length. In addition, we measured for the first time environmentally and spectroscopically relevant self-broadening and nitrogen-broadening coefficients for CO2 and CO in this spectral region and we discuss different possibilities for increasing the sensitivity of the apparatus.

Absolute Rovibrational Line Intensities in the ν 5 Band System of Cyanogen, NCCN

The far-infrared spectrum of the lowest-lying rovibrational band system ν 5 of cyanogen, NCCN, was measured in the wavenumber range from 180 to 280 cm −1. A Fourier transform interferometer was used. Absolute rovibrational line intensities of the fundamental and the first hot band were evaluated. The pure vibrational transition moment matrix elements for the fundamental and the first hot band, |〈μ (00),(01) vib〉| and |〈μ (01),(02) vib〉|, were determined to be 0.1812(19) and 0.1790(30) D, respectively. Furthermore, four nitrogen-broadened spectra of this band system were measured in the pressure range between p N 2 = 8 and 30 mbar (0.1 mbar cyanogen), yielding a nitrogen-broadening coefficient of 0.12 cm −1/atm decreasing slightly with increasing rotational quantum number J. No pressure-induced shifts of line positions were observed in this pressure range. The effects of instrumental distortion on line intensities are discussed.

Measurements of pressure broadening and pressure shifting by nitrogen in the ν1 and ν3 bands of H 216O

Lorentz nitrogen-broadening coefficients and nitrogen pressure-induced shift coefficients have been measured for six lines in the ν 1 band and 98 lines in the ν 3 band of H 2 16O. The results were obtained from analysis of 10 high-resolution (0.01 cm −1) infrared absorption spectra recorded at room temperature using the McMath Fourier transform spectrometer of the National Solar Observatory on Kitt Peak. The analysis was performed using a nonlinear least-squares spectrum fitting procedure. The measured nitrogen-broadening coefficients ranged from ∼0.04 to ∼0.104 cm −1 atm −1, while the nitrogen pressure-induced shift coefficients varied between ∼+0.004 and ∼−0.011 cm −1 atm −1. The majority of the measured pressure-induced shift coefficients (>90%) were found to be negative. The results are compared with previous values reported in the literature, where available.

Measurements of Lorentz-broadening coefficients and pressure-induced line shift coefficients in the ν2 band of HD 16O

Abstract Room temperature Lorentz-broadening coefficients and pressure-induced line shift coefficients in air, nitrogen, and oxygen have been determined for 126 transitions in the ν 2 band of D 2 16 O from laboratory spectra recorded at 0.0053-cm −1 resolution with a Fourier transform spectrometer. Samples of D 2 O + HDO + H 2 O at low pressure (≤1 Torr) and lean mixtures of D 2 O + HDO + H 2 O broadened by nitrogen, oxygen, and air were used in the experiments. Transitions up to J ″ = 12 were measured using a nonlinear least-squares fitting procedure assuming a Voigt line profile. The broadening coefficients obtained for the three buffer gases generally decrease with increasing J ″. The ratio of the nitrogen-broadening coefficient to the corresponding oxygen-broadening coefficient is correlated with the magnitude of the oxygen-broadening coefficient (the narrower lines have the larger N 2 -to-O 2 broadening ratios). The pressure-shift coefficients are both positive and negative with values in the range −0.008 to +0.008 cm −1 atm −1 ; no significant correlation with the widths was found. The results are compared with previously reported measurements.

Measurements of Lorentz-broadening coefficients and pressure-induced line shift coefficients in the ν2 band of D 216O

Room temperature Lorentz-broadening coefficients and pressure-induced line shift coefficients in air, nitrogen, and oxygen have been determined for 126 transitions in the ν 2 band of D 2 16O from laboratory spectra recorded at 0.0053-cm −1 resolution with a Fourier transform spectrometer. Samples of D 2O + HDO + H 2O at low pressure (≤1 Torr) and lean mixtures of D 2O + HDO + H 2O broadened by nitrogen, oxygen, and air were used in the experiments. Transitions up to J″ = 12 were measured using a nonlinear least-squares fitting procedure assuming a Voigt line profile. The broadening coefficients obtained for the three buffer gases generally decrease with increasing J″. The ratio of the nitrogen-broadening coefficient to the corresponding oxygen-broadening coefficient is correlated with the magnitude of the oxygen-broadening coefficient (the narrower lines have the larger N 2-to-O 2 broadening ratios). The pressure-shift coefficients are both positive and negative with values in the range −0.008 to +0.008 cm −1 atm −1; no significant correlation with the widths was found. The results are compared with previously reported measurements.

Intensities in the ν4 band of 15NH 3

Line intensities and nitrogen-broadening coefficients of 33 transitions in the ν 4 band of 15NH 3 have been measured using a diode laser spectrometer. The interpretation of the strongly perturbed line intensities was based on the third-order theory of linestrengths of axially symmetric XY 3 molecules. The analysis yields effective transition moments and the vibrational band strengths of the ν 4 band. It was also possible to determine parameters of the “2, 2” l-type interaction in the ν 4 state.

Transition dipole matrix elements for 14NH 3 from the line intensities of the 2 ν2 and ν4 bands

Line intensities as well as self- and nitrogen-broadening coefficients have been determined for 20 transitions in the 2 ν 2 and ν 4 bands of 14NH 3 using a diode laser spectrometer. Vibrational-inversional transition moments have been determined for transitions from the ground state to the ν 2, 2 ν 2 and ν 4 states by a least-squares fit to the line intensities, taking into account Coriolis and l-type interactions between the nν 2 ( n = 1, 2, 3), ν 4 and ν 2 + ν 4 states [Š. Urban, V. Špirko, D. Papoušek, R. S. McDowell, N. G. Nereson, S. P. Belov, L. I. Gershtein, A. V. Maslovskij, A. F. Krupnov, J. Curtis, and K. Narahari Rao, J. Mol. Spectrosc. 79, 455–495 (1980)]. The values of these transition moments have been combined with the previously obtained transition moments for NH 3 and its isotopomers to obtain an improved fit to the μ z component of the electric dipole moment function of ammonia [cf. V. Špirko, J. Mol. Spectrosc. 74, 456–464 (1979)].