This paper describes the contents of the 2016 edition of the HITRAN molecular spectroscopic compilation. The new edition replaces the previous HITRAN edition of 2012 and its updates during the intervening years. The HITRAN molecular absorption compilation is composed of five major components: the traditional line-by-line spectroscopic parameters required for high-resolution radiative-transfer codes, infrared absorption cross-sections for molecules not yet amenable to representation in a line-by-line form, collision-induced absorption data, aerosol indices of refraction, and general tables such as partition sums that apply globally to the data. The new HITRAN is greatly extended in terms of accuracy, spectral coverage, additional absorption phenomena, added line-shape formalisms, and validity. Moreover, molecules, isotopologues, and perturbing gases have been added that address the issues of atmospheres beyond the Earth. Of considerable note, experimental IR cross-sections for almost 300 additional molecules important in different areas of atmospheric science have been added to the database. The compilation can be accessed through www.hitran.org. Most of the HITRAN data have now been cast into an underlying relational database structure that offers many advantages over the long-standing sequential text-based structure. The new structure empowers the user in many ways. It enables the incorporation of an extended set of fundamental parameters per transition, sophisticated line-shape formalisms, easy user-defined output formats, and very convenient searching, filtering, and plotting of data. A powerful application programming interface making use of structured query language (SQL) features for higher-level applications of HITRAN is also provided.

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The HITRAN 2008 molecular spectroscopic database

Infrared laser-absorption sensing for combustion gases

The averaging effect of velocity-changing collisions reduces the Doppler broadening of isolated spectral lines and leads to one type of collisional narrowing. We present four collisionally narrowed profiles in standardized form using dimensionless parameters and estimate the quantitative effect of narrowing on the spectral line shape in terms of the magnitudes of these parameters. We show that a collisionally narrowed profile fitted by a Voigt function exhibits a characteristic signature on a plot of the residual errors in the fit. This provides a simple test for detectable narrowing effects. One of the simpler and better known models which includes collisional narrowing is the Galatry profile. We present sample plots of the residual errors resulting when theoretical profiles computed from other more elaborate models are fitted by a Galatry function.

Collisional narrowing effects on spectral line shapes measured at high resolution.

We demonstrate that a previously proposed model opens the route for the inclusion of refined non-Voigt profiles in spectroscopic databases and atmospheric radiative transfer codes. Indeed, this model fulfills many essential requirements: (i) it takes both velocity changes and the speed dependences of the pressure-broadening and -shifting coefficients into account. (ii) It leads to accurate descriptions of the line shapes of very different molecular systems. Tests made for pure H2, CO2 and O2 and for H2O diluted in N2 show that residuals are down to ≃ 0.2 % of the peak absorption, (except for the untypical system of H2 where a maximum residual of ±3% is reached), thus fulfilling the precision requirements of the most demanding remote sensing experiments. (iii) It is based on a limited set of parameters for each absorption line that have known dependences on pressure and can thus be stored in databases. (iv) Its calculation requires very reasonable computer costs, only a few times higher than that of a usual Voigt profile. Its inclusion in radiative transfer codes will thus induce bearable CPU time increases. (v) It can be extended in order to take line-mixing effects into account, at least within the so-called first-order approximation.

An isolated line-shape model to go beyond the Voigt profile in spectroscopic databases and radiative transfer codes

The availability of new lasers in the nearand mid infrared spectral region has led to the development of sensors for gas measurements that are now applied extensively in the process industries. Based on tunable diode laser absorption spectroscopy (TOLAS) molecules like O2, CH* H2O, CO, CO2, NH3, HC1 and HF can be detected in-situ with high selectivity and sensitivity in continuous, real time operation. Using sensitive detection techniques like wavelength modulation spectroscopy (WMS), often low ppb and ppm concentration measurements with Is integration time are feasible. Detection limits can be improved by using extractive sampling and a long multi-pass cell. TOLAS has become an accepted technique in the process industries for difficult measurement tasks, because it is compatible with high temperatures, pressures, dust levels and corrosive media. Gas concentrations, temperatures, velocities and pressures can be determined. TOLAS is used widely for continuous emission monitoring and process control with over 1,000 field instruments worldwide. In this article, after an introduction to the basics of TOLAS, several interesting applications and installations in various process industrial units with some examples from other industries are reviewed.

Tunable diode laser absorption spectroscopy (tdlas) in the process industries – a review

By using the classical Fourier integral theory, an expression is given for the shape of a spectral line, broadened by phase changes due to collisions and by the actual changes in velocity of the emitting particles resulting from collisions. The result is not a simple Voigt-type folding of an exponential into a dispersion distribution; it exhibits the contraction noted by Dicke and leads to the usual formulas when the time interval between path-deflecting or phase-disturbing collisions becomes very great.

Louis Galatry

Papers

Simultaneous Effect of Doppler and Foreign Gas Broadening on Spectral Lines