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• We performed calculations of N 2 -, O 2 -, and air-broadened halfwidths of CH 3 CN lines. • We derived the temperature exponent. • The methods account for the k-degeneracy of symmetric-top molecular lines. • The RRB with LM method incorporates both line coupling and line mixing effects. • The RRB with LM method yields a very good agreement with measurements in the qR and qP branches. The N 2 -, O 2 , and air-broadened halfwidths of CH 3 CN lines in the parallel ν 4 band have been calculated, along with the relaxation matrices W. These calculations employ our modified and refined versions of the Robert-Bonamy formalism and use all potential parameters from the literature without adjustments. Extensive comparisons between the predicted N 2 -broadened halfwidths in the qR and qP branches from the models at T = 296 K and experimental measurements are presented, showing that our latest model very closely matches the measurements. For the qQ branch, where measurements are unavailable, we compare our N 2 -broadened halfwidths with the converted air-broadened data from HITRAN 2008, obtaining similarly good agreement. The variation in the j and k dependencies of the N 2 -broadened halfwidths is discussed in detail. Additionally, the theoretically determined conversion factor from N 2 - to air-broadening is provided. Finally, based on our theoretical calculations of N 2 -broadened halfwidths of the qR(j,3) lines at five different temperatures, ranging from 250 K to 350 K, the temperature exponent N is determined and its dependence on j is analyzed. [ABSTRACT FROM AUTHOR]

• We conducted an analysis on the branch dependence of N2-brodened halfwidths of CH3Br lines. • The methods consider the k-degeneracy of symmetric-top molecular lines. • The RRB with LM method addresses both line coupling and line mixing effects. • The RRB with LM method yields a very good agreement with measurements at temperatures of 296 K. The N 2 -broadened halfwidths of CH 3 Br in the ν 6 band have been calculated, along with the relaxation matrices W. These calculations employ our modified and refined versions of the Robert-Bonamy formalism. Extensive comparisons between the predicted halfwidths from the models and experimental measurements at T = 296 K are presented. Our latest model very closely matches the measurements. Meanwhile, we considered line mixing effects in the spectral profile of the RQ(j,0) sub-branch. Our method probably yields too large values of the off-diagonal elements of W. Finally, by comparing our calculated halfwidths with the data in HITRAN, we have observed generally good agreement, especially for lines with high values of j. However, the agreement becomes poor for lines with low values of j, deteriorating as j decreases. We identified a factor contributing to this poor agreement: the neglect of branch dependence in the development of HITRAN data. We believe that for lines with low values of j, this oversight undermines the reliability of the halfwidth values of CH 3 Br in HITRAN. [ABSTRACT FROM AUTHOR]

• The j and k dependencies of line coupling and line mixing effects of CH 3 F-N 2 have been exhibited. • The method considers the k-degeneracy of symmetric-top molecular lines. • The method considers both line coupling and line mixing effects. • This approach yields a very good agreement with measurements at temperatures of 296 K and 183 K. The N 2 -broadening halfwidths of CH 3 F in the ν 5 and ν 6 perpendicular bands have been calculated, along with their temperature exponents. These calculations utilize a modified and refined version of the Robert-Bonamy formalism, developed by the current authors within a semi-classical line shape framework. Extensive comparisons between the predicted halfwidths from the model and experimental measurements at 296 K and 183 K are presented. Our latest model accurately predicts the dependencies of the halfwidths on both the j and k quantum numbers. Furthermore, by extending our calculations to two additional temperatures, namely 240 K and 350 K, the temperature exponent N is determined for various sub-branches. The dependencies of N on j and k are analyzed, and theoretical explanations are provided to elucidate the predicted behaviors of N. [ABSTRACT FROM AUTHOR]

Line coupling and line mixing effects have been calculated for several self-broadened NH 3 lines in parallel bands involving an excited ν 2 mode. It is well known that once the ν 2 mode is excited, the inversion splitting quickly increases as this quantum number increases. In the present study, we have shown that the ν 2 dependence of the inversion splitting plays a dominant role in the calculated line-shape parameters. For the ν 2 band with a 36 cm −1 splitting, the intra-doublet couplings practically disappear and for the 2ν 2 and 2ν 2 - ν 2 bands with much higher splitting values, they are completely absent. With respect to the inter-doublet coupling, it becomes the most efficient coupling mechanism for the ν 2 band, but it is also completely absent for bands with higher ν 2 quantum numbers. Because line mixing is caused by line coupling, the above conclusions on line coupling are also applicable for line mixing. Concerning the check of our calculated line mixing effects, while the present formalism has well explained the line mixing signatures observed in the ν 1 band, there are large discrepancies between the measured Rosenkranz mixing parameters and our calculated results for the ν 2 and 2ν 2 bands. In order to clarify these discrepancies, we propose to make some new measurements. In addition, we have calculated self-broadened half-widths in the ν 2 and 2ν 2 bands and made comparisons with several measurements and with the values listed in HITRAN 2012. In general, the agreements with measurements are very good. In contrast, the agreement with HITRAN 2012 is poor, indicating that the empirical formula used to predict the HITRAN 2012 data has to be updated. [ABSTRACT FROM AUTHOR]

• The j and k dependencies of line coupling and line mixing effects of CH 3 D-N 2 have been exhibited. • The method takes into account the k-degeneracy of symmetric-top molecular lines. • The method takes into account the line coupling and line mixing effects. • It leads to a reasonable agreement with measurements. Line coupling and line mixing effects in parallel and perpendicular bands of CH 3 D perturbed by N 2 have been studied. The work focuses on exhibiting the j and k dependencies of these two processes. The calculations were based on a previously reported anisotropic intermolecular potential including both the long-range multipole, induction, and dispersion forces and a short-range atom-atom model. It is shown that components with L 1 = 3 of the atom-atom model are dominant contributions to the diffusion operator. As a consequence, in comparison with other molecular systems such as the CH 3 Cl-N 2 and CH 3 I-N 2 , theoretically predicted line coupling and line mixing effects exhibit completely new j and k dependencies. In general, the theoretically calculated halfwidths and intra-doublets' off-diagonal elements of the relaxation matrix are in reasonable agreement with measurements. [ABSTRACT FROM AUTHOR]

Transmission spectra in the fundamental bands of H 2 and N 2 gas inside the pores of a silica aerogel sample were recorded at room temperature and for several pressures using a Fourier transform spectrometer. They first show that, as the absorption is proportional to the pressure, it is due to the interactions of the molecules with the inner surfaces of the pores and not to the dipole induced during gas-phase molecule–molecule collisions. Furthermore, the analysis of the widths and areas of the observed absorption structures indicate that, for the considered aerogel sample, most of the absorption is likely due to “free” molecules moving within the pores with a weak contribution of adsorbed molecules. [ABSTRACT FROM AUTHOR]

• Line coupling and line mixing in CH 3 I spectra perturbed by N 2 and O 2 have been calculated. • The semi-classical method correctly takes into account the k-degeneracy of the transitions. • It leads to a reasonable agreement with the available data, including the T-dependence. • New experiments at higher pressures are suggested to check the description of inter-doublets couplings. Calculations of the N 2 -, O 2 -, and air-broadened widths, together with their temperature dependence exponents have been made for transitions of CH 3 I in the ν 5 and ν 6 bands. The calculations are based on a semi-classical line shape formalism developed by the current authors through modifying and refining the Robert-Bonamy formalism. In recent years, we have applied this formalism for linear molecules, symmetric-top molecules with inversion symmetry, and asymmetric-top molecules. For symmetric-top molecules with the k degeneracy such as CH 3 I, the formalism has a new feature. In this case, one should consider each of the CH 3 I transitions labeled by k i or f ≠ 0 as a doublet. Then, one needs to consider the effects of the line mixing process between these two components. Comparisons of our theoretical predictions with some data available demonstrate a very reasonable agreement. Finally we propose new experiments at higher perturber pressures that would enable one to check the theoretically calculated relaxation matrices and to extend the analysis to the inter-doublet mixing effects. [ABSTRACT FROM AUTHOR]

Abstract: Precise modelling of infrared absorption by carbon dioxide is of primary importance for radiative transfer calculations in CO2-rich atmospheres like those of Venus and Mars. Despite various measurements and theoretical models dedicated to this subject, accurate data at different temperatures and pressures are still lacking in numerous spectral regions. In this work, using two Fourier Transform Spectrometers, we have measured spectra of pure CO2 in a large spectral region range, from 750 to 8500cm−1 at various densities (3–57amagat) and temperatures (230–473K). Comparisons between measured dipolar absorption bands and spectra calculated with the widely used Lorentz line shape show very large discrepancies. This result is expected since the Lorentz approach neglects line-coupling effects due to intermolecular collisions which transfer absorption from the wings to the band center. In order to account for this effect, a theoretical approach based on the impact and Energy Corrected Sudden approximations has been developed. Comparisons of this model with numerous laboratory spectra in a wide range of pressure, temperature and spectral domain show satisfactory agreements for band centers and near wing regions where the impact approximation is valid. However, as expected, due to the breakdown of the impact approximation, the model fails when considering far wing regions. In the absence of precise models accounting for line-mixing and finite collision duration (non impact) effects, empirical approximations are proposed in order to model the far wings. [Copyright &y& Elsevier]

Abstract: The influence of line-mixing on the emission by Mars’ atmosphere is studied using a model based on the energy corrected sudden approximation. Comparisons between the forward calculations of brightness temperatures and the values measured by the short-wavelength spectrometer of the infrared space observatory are presented. These indicate that line-mixing effects, although not negligible—particularly near Q branches—are quite small and fall within the uncertainty range due to noise, model and measurements errors. [Copyright &y& Elsevier]

Temperature (200–300 K) and pressure (70–200 atm) dependent laboratory measurements of infrared transmission by CO2–N2 mixtures have been made. From these experiments the absorption coefficient is reconstructed, over a range of several orders of magnitude, between 600 and 1000 cm-1. The elevated densities used in the experiments (up to 200 atm) magnify the contribution of the wings of the ν2 band lines. In order to analyze the spectra, a theoretical model based on the energy corrected sudden approximation is proposed which accounts for line-mixing effects within the impact approximation. This approach uses the model and associated parameters built previously to model Q branches (JQSRT 1999;61:153) but extends it by now including all P, Q, and R lines. No adjustable parameters are used and fundamental properties of the collisional relaxation operator are verified by using a renormalization procedure. Comparisons between measured and calculated spectra confirm that neglecting line-mixing (Lorentzian model) leads to an overestimation of absorption by up to three orders of magnitude in the far wings. On the other hand, the proposed approach leads to satisfactory results both in regions dominated by contributions of local lines and in the wing: measured spectra are correctly modeled over a range where absorption varies by more than four orders of magnitude. The largest discrepancies, which appear about 150 cm-1 from the ν2 center, can be due to finite duration of collisions effects or to uncertainties in the experimental determination of very weak absorption. [Copyright &y& Elsevier]

The translation-rotation collision-induced spectra of N2–N2, O2–O2 and N2–O2 mixtures are calculated theoretically. For N2–N2, using the matrix elements for the quadrupole and hexadecapole moments and the isotropic and anisotropic polarizabilities obtained previously from a global analysis of the fundamental band spectra, we obtain numerical values for the zeroth moment that are smaller than the measured values by 9–14%, depending on the temperature. By increasing the value for the matrix element of the isotropic polarizability slightly, good agreement with experiment is obtained. For O2–O2, the theoretical spectrum is significantly smaller than the experimental result. By increasing the matrix element of the hexadecapole moment by a factor of 1.7, we can obtain good agreement. This larger value for the hexadecapole moment will not appreciably affect the agreement found previously in the fundamental region because the hexadecapole contribution to the intensity is very small, unlike the translation-rotation band where it is larger than the contribution due to the quadrupole moment. Using these parameters, we then calculate the collision-induced absorption for N2–O2 mixtures for which no experimental data exist. Finally, we calculate the collision-induced absorption for air, and compare our results with previous work; we express the results for the ratio of the absorption coefficient of air to that of N2–N2 as a function of wavenumber and temperature, R(ω,T), which can easily be implemented in atmospheric models. [Copyright &y& Elsevier]

• Line mixing of CH 3 Cl-N 2 has been calculated from a potential including short range forces. • The semi-classical model takes into account the k-degeneracy of the transitions. • A new difficulty appears in the calculation when an atom-atom potential model is added. • A pragmatic method allows to by-pass that problem. • It leads to a good agreement with the available data. Line coupling and line mixing effects of CH 3 Cl lines in the ν 1 band perturbed by N 2 have been investigated. We have taken into account the non-diagonality of the exp(−S 2) operator within specified line spaces as well as the k-degeneracy of the transitions (due to the double degeneracy of the j,k levels with k ≠ 0). These transitions should be considered as doublets coupled by the line mixing process. A new problem appears in the calculation when the atom-atom potential model is introduced. In order to overcome this difficulty, a pragmatic approach is proposed. Comparisons of theoretically calculated matrix elements of W with measurements of QR(j,k) doublets as well as some QQ k sub-branches, which are strongly affected by line mixing, have been made. The results show that the formalism improved in this way leads to rather accurate predictions. [ABSTRACT FROM AUTHOR]

• Spectra of CO 2 -H 2 mixtures have been recorded at room temperature by CRDS. • Four spectral windows are covered in the 2.12–2.35 µm spectral region. • The binary coefficients B C O 2 − H 2 + B H 2 − C O 2 have been retrieved from the spectra. • The retrieved binary coefficients are compared to semi-empirical calculations. • This comparison shows the limits of the model in the studied spectral region. Spectra of CO 2 + H 2 mixtures have been recorded at room temperature by using the cavity ring down technique, for four spectral intervals in the 2.12–2.35 µm CO 2 transparency window which is within the (1-0) band of H 2. The binary coefficients B C O 2 − H 2 + B H 2 − C O 2 have been retrieved from the spectra recorded at different pressures after subtraction of the CO 2 monomer contribution and of the H 2 -H 2 and CO 2 -CO 2 collision induced absorptions (CIAs). In order to reduce the uncertainties, new measurement of the pure H 2 CIA, the main subtracted contribution, at the percent level are also reported. The new set of experimental binary coefficients is compared to values provided by semi-empirical calculations made with the assumption of an isotropic CO 2 -H 2 interaction potential and neglecting the short-range interaction-induced electric dipole. This comparison shows the limits of using such a model, which is the only one available, in that spectral region. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Infrared transmission spectra of several molecular gases inside three porous silica samples with pore sizes ranging from 7 nm to several tens of nm have been recorded with a Fourier transform spectrometer. Their analysis shows that consistent values of the percentage of open porosity and average pore size can be retrieved from these non intrusive nor destructive optical measurements. The samples have also been characterized using mercury intrusion/extrusion and the nitrogen sorption method. The results of these different probing techniques are in good agreement when the methods used are adapted to the involved pore size. This consistency demonstrates that light absorption by confined gases is a valuable porosimetry tool. [ABSTRACT FROM AUTHOR]

Reflection spectra of pure CO 2 gas have been recorded in the 4.3 μ m region by using a high resolution Fourier transform spectrometer, providing measured values of the refractive index. Comparisons with the results of calculations using available spectroscopic data, and free of any adjusted line parameter, show a very good agreement. This confirms that this experimental technique provides an alternative approach for the test or determination of spectroscopic parameters. Its advantages for studies of extremely strongly absorbing species and investigations of spatially (tightly) confined molecular gases are discussed. [ABSTRACT FROM AUTHOR]

Abstract: Precise profiles of the 60-GHz molecular oxygen band recorded earlier in a wide temperature range by means of a resonator spectrometer at atmospheric pressure were treated. High signal-to-noise ratio allows careful study of the band shape taking into consideration the mixing effect. Comparative analysis of the band profile calculated by an extended MPM (Millimeter-wave Propagation Model) and by the ECS (Energy Corrected Sudden) approximation model is presented. Some limitations of the MPM approach are discussed on the basis of the comparison of the two models. Interbranch coupling is shown to make a noticeable contribution to absorption which means that it should be taken into account as it is expected to improve band profile modeling accuracy. [Copyright &y& Elsevier]

Abstract: The lack of ionizing radiation use in MRI makes the high spatial resolution technique very appealing. Also, the easy access to multiplanar imaging and the fact that gadolinium-DTPA is well tolerated and not nephrotoxic makes MRI a robust alternative in the healthy as well as the renal compromised patient. Furthermore, MRI adds advanced possibility for tissue characterization and pathology detection and dynamic imaging can be performed. Specific contrast agents specific to the hepatobiliary or the reticuloendothelial system can help with additional information in problem cases. The role of MRI for different organs is discussed and a review of the literature is given. We concluded that MRI is considered a useful and non-invasive diagnostic tool for the detection of hepatic iron concentration, to correct misdiagnosis (pseudolesions) from US and CT in focal steatosis and to help with focal lesion detection and characterization, in the healthy and especially in the cirrhotic liver, where MRI is superior to CT. Moreover, MRCP is excellent for identifying the presence and the level of biliary obstruction in malignant invasion and is considered in the literature as a non-invasive screening tool for common bile duct stones, appropriately selecting candidates for preoperative ERCP and sparing others the need for an endoscopic procedure with its associated complications. MRI is the first choice modality for adrenal evaluation in contemporary medical imaging. It is a useful examination in renal as well as splenic pathology and best assesses loco-regional staging, i.e. arterial involvement in pancreatic cancer. [Copyright &y& Elsevier]

Abstract: We have found an invalid assumption in the Robert–Bonamy formalism that has been widely used for calculating Lorentzian spectral line half-widths and shifts for decades. The problem results in their derivation where they assumed the cumulant expansion can be used to evaluate the Liouville matrix element . At first sight, their assumption appears to be correct because this matrix element is diagonal in the Liouville space and as a result, it looks like that a basic requirement in applying the cumulant expansion is satisfied. However, by decomposing it into two Hilbert matrix elements associated with S I and S F , respectively, we have found that neither of these is diagonal in Hilbert space. Therefore, their assumption is not valid and their expressions for the half-widths and shifts are incorrect. We have found by choosing an average over the internal degrees of the bath molecule as the average in the cumulant expansion, one is able to apply this expansion properly and obtain the correct expressions. Numerical calculations show new half-width and shift values differ from previous ones, and the stronger the interaction between two molecules is, the larger these differences are. [Copyright &y& Elsevier]

Abstract: We present new experimental data on the collision-induced fundamental absorption in N2–H2 mixtures at room temperature and at low enough pressures so that the binary contribution is dominant. Previous measurements have been made at pressures where the ternary and possibly higher absorption coefficients are significant, and this makes it difficult to obtain accurate values for the binary absorption enhancement coefficient. To obtain the enhancement spectrum from the measurements of the mixture, it is necessary to subtract out both the spectra of pure H2 and N2, along with some CO2 impurities thus increasing the experimental uncertainty. Nevertheless, we obtain a value for the integrated intensity of 1.15×10−4 cm−2 amagat−2 that is in good agreement with the previous value of 1.38×10−4. We also discuss how one can scale this result to high temperatures for application to brown dwarf or methane dwarf atmospheres. [Copyright &y& Elsevier]

Abstract: Pressure-broadening and -shifting coefficients of pure HI at room temperature have been determined from fits of high-resolution Fourier transform spectra in the fundamental and first overtone infrared bands. The results indicate that the measured widths are almost identical in both bands and decrease significantly with the rotational quantum number. On the contrary, the pressure-induced shifts show a strong dependence on both the rotational and vibrational states. These results are compared with predictions of a semi-classical model. The latter leads to calculated values in good agreement with measurements and shows that the broadening is dominated by electrostatic interactions due to the (permanent) electric dipole and quadrupole moments. On the contrary, the observed shifts cannot be explained without the introduction of a significant vibrationally dependent isotropic potential. The effects of line coupling between hyperfine components are also discussed although they are expected to be small and cannot be observed from the measured spectra. Finally, some tabulated values of calculated widths and shifts vs. quantum numbers and temperature are proposed. They should be useful for infrared sounding of HI amounts, particularly in the monitoring of the hydrogen production through the sulfur–iodine thermochemical cycle. [Copyright &y& Elsevier]

Abstract: Theoretical calculations are made for the collision-induced electronic absorption in the atmospheric infrared a←X (0,0) and visible b←X (0,0) bands of oxygen in O2–N2 and O2–CO2 pairs. We consider only the long-range quadrupolar induction mechanism and use ab initio values for the quadrupole transition matrix elements that arise from spin-orbit mixing. By fitting the experimental value for the a←X (0,0) absorption in O2–N2, we obtain estimates for the isotropic and anisotropic polarizability electronic transition matrix elements of O2. As a check, we then use these results together with other known data to calculate the corresponding absorption for O2–CO2. We find good agreement, considering experimental error and theoretical approximations. We then estimate the corresponding absorption for the b←X (0,0) absorption in O2–N2. We discuss briefly the observed collision-induced absorption by O2–O2 pairs, and conclude that there must be other induction mechanisms involved for this system. Because of the importance of absorption by O2 in the Earth''s atmosphere, we conclude that a systematic study, including both additional measurements and theoretical analyses must be carried out before a satisfactory understanding can be attained. [Copyright &y& Elsevier]

We report the results of laboratory investigations of the shape of the diagnostic atmospheric N = 1- oxygen line performed over a very wide range of pressures from 0.4 to 1000 Torr using two principally different spectrometers having complementary abilities. A spectrometer with a radio-acoustic detector of absorption was used for recording low pressure spectra spanning the 0.4–2 Torr range, and high pressure data from 250 to 1000 Torr were registered by a resonator spectrometer. The sensitivity of both instruments was improved significantly which allowed us to obtain signal-to-noise ratio at spectra recordings of the order of a few thousands. The spectra analysis enabled the first manifestation of the speed-dependence of the collision cross section of the line, along with considerable refinement of other parameters, including pressure broadening, intensity and line-mixing. The results are of primary importance for atmospheric applications. [ABSTRACT FROM AUTHOR]