Linewidths of ammonia in collisions with He: Calculations from an ab initio potential

We present semiclassical calculations based on the Robert-Bonamy formalism of collisional broadening coefficients of ammonia by collision with He at room temperature. Calculations have been performed with the accurate ab initio potential of Hodges and Wheatley. The calculated line widths are compared to the available experimental data and a satisfactory agreement is found, although the model contains no adjustable parameters. However the calculations also exaggerate the K dependence of the broadenings, especially for lines with K = J − 1 or K = J.     

H2-broadening,shifting and mixing coefficients of the doublets in the ν2 and ν4 bands of PH3 at room temperature

The broadening, shifting and mixing coefficients of the doublet spectral lines in the ν₂ and ν₄ bands of PH₃ perturbed by H₂ have been determined at room temperature. Indeed, the collisional spectroscopic parameters: intensities, line widths, line shifts and line mixing parameters, are all grouped together in the collisional relaxation matrix. To analyse the collisional process and physical effects on spectra of phosphine (PH₃), we have used the measurements carried out using a tunable diode-laser spectrometer in the ν₂ and ν₄ bands of PH₃ perturbed by hydrogen (H₂) at room temperature. The recorded spectra are fitted by the Voigt profile and the speed-dependent uncorrelated hard collision model of Rautian and Sobelman. These profiles are developed in the studies of isolated lines and are modified to account for the line mixing effects in the overlapping lines. The line widths, line shifts and line mixing parameters are given for six A₁ and A₂ doublet lines with quantum numbers K = 3n,?(n = 1,?2, …) and overlapped by collisional broadening at pressures of less than 50 mbar.     

Pressure Shifts and Pressure Broadening of the B and γ Bands of Oxygen

Measurements of pressure shift and pressure broadening in molecular oxygen have been made for rotational transitions in the B (1←0) and γ (2←0) vibrational bands of the b¹Σ⁺_g←X³Σ⁻_g visible electronic transition. The absorption features were measured simultaneously in two cells by photoacoustic spectroscopy using a scanning dye laser. The measurements were made with background gases of both pure oxygen and air at room temperature. The pressure shifts were all negative. The measurements show the magnitude of the pressure shift increasing with vibrational quantum number when compared with existing data for the A (0←0) band. The shifts also increase with rotational number within each vibrational band. The shifts in air are larger than in oxygen although the difference gets smaller with vibrational number. The average shifts in air for the A, B, and γ bands were 36, 11, and 0.2% higher, respectively, than in pure oxygen. The pressure broadening of the rotational lines does not change significantly with vibrational number and in general decreases with rotational number within a band. The pressure shift measurements were used by the high-resolution Doppler imager (on the Upper Atmospheric Research Satellite) to correct the Doppler wind measurements.     

Submillimeter-wave spectroscopy of HCN in excited vibrational states

Measurements of the rotational spectrum of HCN in excited vibrational states have been extended to higher-J values. The transitions reach J=8←7 around 710 GHz for most vibrational states studied in this investigation and J=22←21 near 2 THz for the (020) and (030) vibrational states. Using a pure sample of gaseous HCN at 350 K, selected states up to one quantum in the C–H stretching vibration at 3311.5 cm⁻¹ have been investigated. Even transitions having two quanta in the C–H stretch could be studied employing a glow discharge in a gas mixture of CH₄ and N₂. Molecular constants in 13 vibrational states have been obtained, several of which have been studied for the first time by rotational spectroscopy. The vibrational temperature in the discharge system is found to be about 1500 K for the stretching vibrational modes and about 600 K for the bending states.     

Lineshape analysis of the J = 3 ← 2 and J = 5 ← 4 rotational transitions of room temperature CO broadened by N2, O2, CO2 and noble gases

Collisional relaxation has been considered for millimeter lines of carbon monoxide at room temperature. Accurate measurements of carbon dioxide- and rare gases-broadened widths have been performed on the J = 3 ← 2 rotational line of ¹²CO by using a video-type spectrometer. Measurements of nitrogen-, oxygen-, and xenon-broadened widths of the J = 5 ← 4 rotational line of ¹³CO were also carried by using a frequency-modulated spectrometer. A lineshape study performed on all the investigated binary systems provide confirmation that Voigt profile is not a suitable model to analyse experimental lines in the millimeter-waves region. On one hand, using this profile in the low pressure range, i.e. in the Doppler regime, the retrieved collisional linewidths do not follow a linear variation with the perturbing gas pressure. On the other hand, regardless of the pressure, lineshapes exhibit a narrowed profile. An accurate analysis of the pressure dependence of relaxation rates show that the Galatry profile is not appropriate and that experimental lineshapes are actually Speed Dependent Voigt profiles. Accurate broadening parameters were retrieved from this profile and compared to previous reported values and predictions calculated from the Robert-Bonamy formalism. Finally a variation of the ratio of relaxation speed dependence to broadening parameters versus relative masses of the collision partners is presented.     

Hydrogen-Broadening Coefficients in the ν5 Band of Acetylene at Low Temperature

H₂-broadening coefficients have been measured for 29 lines of C₂H₂ at 173.2 K in the P and R branches of the ν₅ fundamental band near 13.7 μ m, using a tunable diode-laser spectrometer. These lines were individually fitted with a Voigt and a Rautian profile in order to determine the collisional widths. The resulting broadening coefficients are compared with values calculated from a semiclassical theory performed by considering, in addition to electrostatic interactions, the atom-atom Lennard-Jones model. A satisfactory agreement is obtained but only for low and medium J values. By comparing broadening coefficients at 297 and 173.2 K from a simple power law, the temperature dependence of these broadenings has been determined both experimentally and theoretically.     

Argon-broadening coefficients in the ν5 band of acetylene at room and low temperatures

Ar-broadening coefficients have been measured in the P- and R-branches of the ν₅ fundamental band of C₂H₂ for 30 lines at room temperature and 8 lines at −100 °C, using a tunable diode-laser spectrometer. These lines with J values ranging from 2 to 27 are located in the spectral range 665-795 cm⁻¹. The collisional widths are obtained by fitting each absorption line with three lineshape models: the Voigt profile, the Rautian profile accounting for the Dicke narrowing effect, and a general Rautian profile including the absorber speed-dependent collisional broadening. The latter model provides significantly larger broadening coefficients than the Voigt model. These coefficients are also calculated from a semiclassical theory performed by using a simple intermolecular potential with two adjustable parameters. Finally, the temperature dependence of the broadening coefficients has been determined both experimentally and theoretically.     

Ar-Broadening of isotropic Raman lines in the ν2 band of acetylene

Using a high resolution Raman spectrometer, we have measured Ar-broadening coefficients in the ν₂Q branch of C₂H₂ for 22 lines at 295 K, 20 lines at 174 K, and 16 lines at 134 K. These lines with J values ranging from 1 to 23 are located in the spectral range 1970.9-1974.3 cm⁻¹. The collisional widths are obtained by fitting each spectral line with a Rautian profile. The resulting broadening coefficients are compared with theoretical values arising from close coupling and coupled states calculations. A satisfactory agreement is obtained at room as well as at low temperatures, especially for odd J lines. By comparing broadening coefficients at 295, 174, and 134 K from a simple power law, the temperature dependence of these broadenings has been determined both experimentally, and theoretically.     

Collisional line shifting and broadening in the fundamental P-branch of CO in Ar between 214 and 324 K

The collisional shifts and widths of several P-branch spectral lines in the fundamental band of CO-Ar have been measured at temperatures between 214 and 324 K and pressures between 0.025 and 1 atm. The widths have been determined using a line shape model based on the solution of the transport/relaxation equation for the appropriate off-diagonal element of the density matrix. The model uses a realistic molecular potential energy surface to calculate the speed dependence of the collisional broadening, and a rigid sphere potential to calculate the translational motion. It is found that both the shifting and broadening coefficients follow a power law dependence on the temperature. Additionally, it is demonstrated that studies have tended to overestimate the accuracy of collisional widths when the line shape model used to obtain the widths involves multiple fitted line shape parameters or fails to fit the measured spectra within the experimental noise.     

可见光谱区水汽分子碰撞加宽的理论计算

根据能级的实验数据,采用最小二乘法拟合得到水汽分子(202),(122)和(004)振动态的Watson的Hamiltonian常数值。利用这些常数值和修正的量子傅里叶变换(QFT)(即QFT^*)方法,分别计算了水汽分子(202)带中已有实验数据的一些谱线的氮分子碰撞加宽线宽,以及(202),(122)和(004)带^eR(1,1)支谱线的氮分子碰撞加宽线宽、及线宽的温度依赖关系。与实验结果比较表明,利用拟合方法求得的Hamiltonian常数值是合理的,而且QF 关键词：     

Calculation of line parameters of the ν<Subscript>3</Subscript> band of monodeuterated methane: Nitrogen broadening

Halfwidths and shifts of CH₃D lines are calculated for the case of nitrogen broadening. The calculations are performed for room temperature (296 K) for vibrational–rotational lines in the ν₃ parallel band, with the rotational quantum numbers varying in the ranges of 0 ≤ J ≤ 70 and 0 ≤ K ≤ 20. For each line, the temperature-dependence characteristics are calculated in the range of 200–400 K recommended for the HITRAN database. The calculations are carried out using a semiempirical method with a correction factor the parameters of which are adjusted on a number of experimental values.     

Experimental and theoretical studies of room-temperature sub-millimetre CH3 35Cl line shapes broadened by H2

Hydrogen-broadening coefficients of methyl chloride rotational lines J?=?6?→?7, 10?→?11, 17?→?18, 22?→?23 and 31?→?32 at 296?K are measured as functions of the quantum number K using a sensitive frequency-modulation technique. As expected for this light perturber, the observed line shapes are well described by Voigt profile model. A clear dependence of the collisional broadening on K is observed for most transitions. From a detailed study of the K-components of the transition J?=?6?→?7 situated at 186?GHz no variation of the broadening of the hyperfine components related to ³⁵Cl quadrupole is stated. Given the absence of refined ab initio computed potential energy surfaces and the impracticality of quantum-mechanical calculations for the considered molecular system, theoretical values of these broadening coefficients are estimated by a semi-classical approach with exact trajectories and a model interaction potential including both long-range and short-range (atom-atom) interactions of the active molecule rigorously treated as a symmetric top. It is shown that the short-range forces yield important contributions to the collisional line width for all values of the rotational quantum numbers J and K. Various models are also tested for the isotropic part of the interaction potential which governs the relative translational motion. It is demonstrated that for the very light perturbing molecule H₂ the calculated line widths, practically independent from the rotational quantum number J (for K?≤?J), are particularly sensitive to the position and slope of the repulsive wall. Modifications required in the semi-classical formalism for a correct application of the cumulant expansion are also tested and it is stated that no difference is observed for the CH₃Cl–H₂ system characterised by quite weak interactions.     

Collisional broadening of the J = 1 ← 0 transition of HC15N by nitrogen,oxygen, helium,and air

Nitrogen-broadened linewidths have been measured for the J = 1 ← 0 rotational transition in the fundamental vibrational state of the hydrogen cyanide isotopic species ¹H¹²C¹⁵N, located at 88 055.01 MHz. The data have been recorded for four temperature levels in the range 234–295 K. The collisional half-widths derived from these measurements allowed us to determine, to our knowledge for the first time, the temperature dependence of the foreign gas broadening parameter. Linewidth measurements at room temperature with oxygen, air, and helium as broadening gases are also reported.     

Temperature dependence of pressure broadening of NH3 perturbed by H2 and N2

The temperature dependence of pressure broadening of 134 rovibrational transitions of several branches in the ν₄ and 2ν₂ bands of ammonia perturbed by H₂ and N₂ has been measured using a high-resolution Fourier transform spectrometer. The temperature range covered during the experiments was between 235 and 296 K. The pressure-broadening linewidths were obtained using the method of multipressure fitting to the measured shapes of the lines. These broadenings were also calculated using a semiclassical model leading to a reasonable agreement with the observations and reproduces well the strong systematic experimental J and K quantum number dependencies. The retrieved values of the linewidths, along with those previously determined from the spectra at room temperature, were used to derive the temperature dependence of both H₂ and N₂ broadening of NH₃ lines. The broadening coefficients were shown to fit closely the well-known exponential law. For both experimental and theoretical results, the temperature exponent n has been obtained. Careful inspection of the experimental values shows that, contrary to the linewidths, the coefficient n is nearly K independent within each J multiplet. Also for a given J it does not seem to exhibit any noticeable variation with the type of rotational transition. On the other hand, the calculated n values exhibit a strong J and K systematic dependencies. n increases with K for a given J, decreases with J for a given K and are independent of the type of rotational transition.     

N2- and O2-broadening coefficients in the ν2 and ν5 bands of CH3F at 183 and 298 K

The N₂- and O₂-broadening coefficients of 33 rovibrational lines in the ν₂ and ν₅ bands of ¹²CH₃F were measured at 183 K using a diode-laser spectrometer. The measurement of these coefficients was also realized at room temperature for 10 of these lines to determine their temperature dependence. The line parameters were obtained by fitting to the experimental profile the Voigt lineshape, and the Rautian and Galatry models taking into account the collisional narrowing. Calculations of the pressure-broadening coefficients were also performed for the same temperatures from a semiclassical model involving electrostatic, induction and dispersion interactions in the intermolecular potential. The calculated values reproduce well the experimental data for both temperatures and both perturbers and the theoretical temperature dependence of the broadening coefficients is in satisfactory agreement with that derived from the measurements.     

Temperature dependence of foreign gas broadening of HCl fundamental lines

A long-pathlength variable temperature cell has been used to study three hydrogen chloride 0–1 vibration-rotational lines, P(7), P(8), and P(9) which were broadened by He, Ar, N₂, O₂, and CO at room temperature and by Ar at low temperatures down to 190 K. The method employed to extract the linewidths is the equivalent width method. The temperature dependence of the resulting cross sections for the HClAr broadened lines is similar to that recently found for other argon broadened HCl infrared and microwave lines. The results reported here (for high J lines) complement the other results (for low J lines) and together seem to constitute enough new data for further theoretical attempts at describing the process of collisional broadening in general, and the broadening of HCl by argon in particular.     

N2-broadening coefficients in the ν3 band of CS2 at room and low temperatures

Using a tunable diode-laser spectrometer, N₂-broadening coefficients have been measured for 15 lines in the ν₃ band of C³²S₂ at room and low temperatures (298, 273.2, 248.2, 223.2, and 198.2 K). These lines with J values ranging from 2 to 62 are located in the spectral range 1519-1545 cm⁻¹. The collisional widths are obtained by fitting each measured spectral line with a Voigt and a Rautian lineshape model and for a few lines we also used a Galatry model. From these results, we have determined the n parameter of the temperature dependence of each broadening coefficient. A semiclassical calculation of these broadenings has been performed by considering in addition to the main electrostatic quadrupole-quadrupole interaction an anisotropic dispersion contribution leading to satisfactory results at all temperatures and providing the n temperature dependence parameter in good agreement with the experimental determination.     

Collisional broadening and line intensities in the ν2 and ν4 bands of PH3

Using a tunable diode-laser spectrometer self-broadening coefficients and absolute intensities have been measured for 26 lines of PH₃ at 298 K in the QR branch of the ν₂ band and the PP and RP branches of the ν₄ band. The recorded lines with J values ranging from 2 to 14 and K from 0 to 11 are located in the spectral range 995-1093 cm⁻¹. Self-broadening coefficients have also been measured at 173.4 K for nine of these lines. The collisional widths and line strengths are obtained by fitting each spectral line with different theoretical profiles. The results obtained for the line intensities are in good agreement with recent measurements [J. Mol. Spectrosc. 215 (2002) 178]. The self-broadening coefficients are also calculated on the basis of a simple semiclassical model involving only the electrostatic interactions. A satisfactory agreement is obtained except for high J values or K values equal to J, for which the calculated results are notably underestimated. By comparing broadening coefficients at room and low temperatures, the temperature dependence of these broadenings has been determined both experimentally and theoretically.     

Pressure broadening and shifting parameters for the spectral lines in the first overtone vibration-rotation bands of HBr and HI in mixtures with rare gases

We present experimental data on the previously unknown line broadening and shifting coefficients in the (2 ← 0) overtone vibration-rotation bands of the HBr and HI molecules in mixtures with several rare gases. The vibrational dependence of the isotropic and anisotropic components of the binary interaction potential is probed by separating the measured line shifts into parts symmetric and asymmetric in the line number m and by comparing with the previously published similar data for the fundamental bands of the same molecules. It is shown that the line shifts are dominated by the vibrational dependence of the isotropic potential. A linear correlation is found between the asymptotic values of the symmetric shifts in the overtone bands for all HX-Rg (X = F, Cl, Br, I) pairs and the respective C₆ long-range potential energy constants. Line broadening parameters in the overtone band of pure HBr are also reported.     

Collisional broadening and shifting of OCS rotational spectrum lines

Broadening and shifting of carbonyl sulfide (OCS) rotational spectrum lines by pressure of N₂, O₂ and OCS were accurately studied in the frequency range 24–850 GHz at room temperature using a spectrometer with radio-acoustic detection of absorption. Rotational dependences of collisional widths of OCS spectrum lines were determined by a simple empirical polynomial fit of experimental data. Experimental uncertainties were analyzed. Results of supplementary test measurements of self-broadening of rotational OCS lines in the ν₂ excited vibrational state and carbon monoxide (CO) lines in the ground vibrational state are presented. Comparison of the obtained results with previously known measurements and theoretical calculations is given. The performed work allows for the first time development of accurate gaseous etalon of absorption for atmospheric applications and laboratory use, covering continuously the whole millimeter- and submillimeter-wave range.