HITRAN (an acronym for High Resolution Transmission) molecular spectroscopic database is a compilation of spectroscopic parameters used to simulate and analyze the transmission and emission of light in gaseous media, with an emphasis on planetary atmospheres. The knowledge of spectroscopic parameters for transitions between energy levels in molecules (and atoms) is essential for interpreting and modeling the interaction of radiation (light) within different media.
For half a century, HITRAN has been considered to be an international standard which provides the user a recommended value of parameters for millions of transitions for different molecules. HITRAN includes both experimental and theoretical data which are gathered from a worldwide network of contributors as well as from articles, books, proceedings, databases, theses, reports, presentations, unpublished data, papers in-preparation and private communications. A major effort is then dedicated to evaluating and processing the spectroscopic data. A single transition in HITRAN has many parameters, including a default 160-byte fixed-width format used since HITRAN2004. [1] Wherever possible, the retrieved data are validated against accurate laboratory data. [2]
The original version of HITRAN was compiled by the US Air Force Cambridge Research Laboratories (1960s) in order to enable surveillance of military aircraft detected through the terrestrial atmosphere. [2] One of the early applications of HITRAN was a program called Atmospheric Radiation Measurement (ARM) for the US Department of Energy. [2] In this program spectral atmospheric measurements were made around the globe in order to better understand the balance between the radiant energy that reaches Earth from the sun and the energy that flows from Earth back out to space. [2] The US Department of Transportation also utilized HITRAN in its early days for monitoring the gas emissions (NO, SO2, NO2) of super-sonic transports flying at high altitude. [2] HITRAN was first made publicly available in 1973 [3] and today there are a multitude of ongoing and future NASA satellite missions which incorporate HITRAN. [2] One of the NASA missions currently utilizing HITRAN is the Orbiting Carbon Observatory (OCO) which measures the sources and sinks of CO2 in the global atmosphere. [2] HITRAN is a free resource and is currently maintained and developed at the Center for Astrophysics | Harvard & Smithsonian, Cambridge MA, USA (CFA/HITRAN).
HITRAN is the worldwide standard for calculating or simulating atmospheric molecular transmission and radiance from the microwave through ultraviolet region of the spectrum. [4] The HITRAN database is officially released on a quadrennial basis, with updates posted in the intervening years on HITRANonline. There is a new journal article published in conjunction with the most recent release of the HITRAN database, and users are strongly encouraged to use the most recent edition. [5] Throughout HITRAN's history, there have been around 50,000 unique users of the database and in recent years there are over 24,000 users registered on HITRANonline. There are YouTube tutorials on the HITRANonline webpage to answer frequently asked questions by users. [2]
Data Available from HITRAN |
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Line-by-Line Transitions |
Absorption Cross Sections |
Collision Induced Absorption |
Aerosol Refractive Indices |
HITEMP |
Supplemental data for radiative-transfer calculations [4] |
The current version, HITRAN2020, contains 55 molecules in the line-by-line portion of HITRAN along with some of their most significant isotopologues (144 isotopologues in total). [5] These data are archived as a multitude of high-resolution line transitions, each containing many spectral parameters required for high-resolution simulations.
In addition to the traditional line-by-line spectroscopic absorption parameters, the HITRAN database contains information on absorption cross-sections where the line-by-line parameters are absent or incomplete. Typically HITRAN includes absorption cross-sections for heavy polyatomic molecules (with low-lying vibrational modes) which are difficult for detailed analysis due to the high density of the spectral bands/lines, broadening effects, isomerization, and overall modeling complexity. [6] There are 327 molecular species in the current edition of the database provided as cross-section files. The cross-section files are provided in the HITRAN format described on the official HITRAN website (http://hitran.org/docs/cross-sections-definitions/).
The HITRAN compilation also provides collision-induced absorption (CIA) [7] that was first introduced into HITRAN in the 2012 edition. [8] CIA refers to absorption by transient electric dipoles induced by the interaction between colliding molecules. Instructions for accessing the CIA data files can be found on HITRAN/CIA.
HITRAN2020 also has an aerosols refractive indices section, with data in the visible, infrared, and millimeter spectral ranges of many types of cloud and aerosol particles. Knowledge of the refractive indices of the aerosols and cloud particles and their size distributions is necessary in order to specify their optical properties. [9]
HITEMP is the molecular spectroscopic database analogous to HITRAN for high-temperature modeling of the spectra of molecules in the gas phase. [10] HITEMP encompasses many more bands and transitions than HITRAN for eight absorbers: H2O, CO2, N2O, CO, CH4, NO, NO2 and OH. [10] [11] [12] Due to the extremely large number of transitions required for high-temperature simulations, it was necessary to provide the HITEMP data as separate files to that of HITRAN. The HITEMP line lists retain the same 160-character format that was used for earlier editions of HITRAN. [10] [1] There are numerous applications for HITEMP data, some examples include the thermometry of high-temperature environments, [13] analysis of combustion processes, [14] and modeling spectra of atmospheres in the Solar System, [15] exoplanets, [16] brown dwarfs, [17] and stars. [18]
A Python library HAPI (HITRAN Application Programming Interface) has been developed which serves as a tool for absorption and transmission calculations as well as comparisons of spectroscopic data sets. HAPI extends the functionality of the main site, in particular, for the calculation of spectra using several types of line shape calculations, including the flexible HT (Hartmann-Tran) profile. This HT line shape can also be reduced to a number of conventional line profiles such as Gaussian (Doppler), Lorentzian, Voigt, Rautian, Speed-Dependent Voigt and Speed-Dependent Rautian. In addition to accounting for pressure, temperature and optical path length, the user can include a number of instrumental functions to simulate experimental spectra. HAPI is able to account for broadening of lines due to mixtures of gases as well as make use of all broadening parameters supplied by HITRAN. This includes the traditional broadeners (air, self) as well as additional parameters for CO2, H2O, H2 and He broadening. [19] The following spectral functions can be calculated in the current version #1 of HAPI: [20]
HAPIEST (an acronym for HITRAN Application Programming Interface and Efficient Spectroscopic Tools) is a graphical user interface allowing users to access some of the functionality provided by HAPI without any knowledge of Python programming, including downloading data from HITRAN, and plotting of spectra and cross-sections. The source code for HAPIEST is available on GitHub (HAPIEST), along with binary distributions for Mac and PC.
Infrared spectroscopy is the measurement of the interaction of infrared radiation with matter by absorption, emission, or reflection. It is used to study and identify chemical substances or functional groups in solid, liquid, or gaseous forms. It can be used to characterize new materials or identify and verify known and unknown samples. The method or technique of infrared spectroscopy is conducted with an instrument called an infrared spectrometer which produces an infrared spectrum. An IR spectrum can be visualized in a graph of infrared light absorbance on the vertical axis vs. frequency, wavenumber or wavelength on the horizontal axis. Typical units of wavenumber used in IR spectra are reciprocal centimeters, with the symbol cm−1. Units of IR wavelength are commonly given in micrometers, symbol μm, which are related to the wavenumber in a reciprocal way. A common laboratory instrument that uses this technique is a Fourier transform infrared (FTIR) spectrometer. Two-dimensional IR is also possible as discussed below.
Spectroscopy is the field of study that measures and interprets electromagnetic spectra. In narrower contexts, spectroscopy is the precise study of color as generalized from visible light to all bands of the electromagnetic spectrum.
Ultraviolet (UV) spectroscopy or ultraviolet–visible (UV–VIS) spectrophotometry refers to absorption spectroscopy or reflectance spectroscopy in part of the ultraviolet and the full, adjacent visible regions of the electromagnetic spectrum. Being relatively inexpensive and easily implemented, this methodology is widely used in diverse applied and fundamental applications. The only requirement is that the sample absorb in the UV-Vis region, i.e. be a chromophore. Absorption spectroscopy is complementary to fluorescence spectroscopy. Parameters of interest, besides the wavelength of measurement, are absorbance (A) or transmittance (%T) or reflectance (%R), and its change with time.
A spectral line is a weaker or stronger region in an otherwise uniform and continuous spectrum. It may result from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to identify atoms and molecules. These "fingerprints" can be compared to the previously collected ones of atoms and molecules, and are thus used to identify the atomic and molecular components of stars and planets, which would otherwise be impossible.
Absorption spectroscopy is spectroscopy that involves techniques that measure the absorption of electromagnetic radiation, as a function of frequency or wavelength, due to its interaction with a sample. The sample absorbs energy, i.e., photons, from the radiating field. The intensity of the absorption varies as a function of frequency, and this variation is the absorption spectrum. Absorption spectroscopy is performed across the electromagnetic spectrum.
The Morse potential, named after physicist Philip M. Morse, is a convenient interatomic interaction model for the potential energy of a diatomic molecule. It is a better approximation for the vibrational structure of the molecule than the quantum harmonic oscillator because it explicitly includes the effects of bond breaking, such as the existence of unbound states. It also accounts for the anharmonicity of real bonds and the non-zero transition probability for overtone and combination bands. The Morse potential can also be used to model other interactions such as the interaction between an atom and a surface. Due to its simplicity, it is not used in modern spectroscopy. However, its mathematical form inspired the MLR (Morse/Long-range) potential, which is the most popular potential energy function used for fitting spectroscopic data.
This page provides supplementary chemical data on n-pentane.
Discrete dipole approximation (DDA), also known as coupled dipole approximation, is a method for computing scattering of radiation by particles of arbitrary shape and by periodic structures. Given a target of arbitrary geometry, one seeks to calculate its scattering and absorption properties by an approximation of the continuum target by a finite array of small polarizable dipoles. This technique is used in a variety of applications including nanophotonics, radar scattering, aerosol physics and astrophysics.
An atmospheric radiative transfer model, code, or simulator calculates radiative transfer of electromagnetic radiation through a planetary atmosphere.
The absorption of electromagnetic radiation by water depends on the state of the water.
GEISA - GEISA is a computer-accessible spectroscopic database, designed to facilitate accurate forward radiative transfer calculations using a line-by-line and layer-by-layer approach. It was started in 1974, at Laboratoire de Météorologie Dynamique (LMD) in France. GEISA is maintained by the ARA group at LMD for its scientific part and by the ETHER group at IPSL for its technical part. Currently, GEISA is involved in activities related to the assessment of the capabilities of IASI through the GEISA/IASI database derived from GEISA.
Deuterium-depleted water (DDW) is water which has a lower concentration of deuterium than occurs naturally at sea level on Earth.
Incoherent broad band cavity enhanced absorption spectroscopy (IBBCEAS), sometimes called broadband cavity enhanced extinction spectroscopy (IBBCEES), measures the transmission of light intensity through a stable optical cavity consisting of high reflectance mirrors (typically R>99.9%). The technique is realized using incoherent sources of radiation e.g. Xenon arc lamps, LEDs or supercontinuum (SC) lasers, hence the name.
Spectral line shape describes the form of a feature, observed in spectroscopy, corresponding to an energy change in an atom, molecule or ion. This shape is also referred to as the spectral line profile. Ideal line shapes include Lorentzian, Gaussian and Voigt functions, whose parameters are the line position, maximum height and half-width. Actual line shapes are determined principally by Doppler, collision and proximity broadening. For each system the half-width of the shape function varies with temperature, pressure and phase. A knowledge of shape function is needed for spectroscopic curve fitting and deconvolution.
In spectroscopy, collision-induced absorption and emission refers to spectral features generated by inelastic collisions of molecules in a gas. Such inelastic collisions may induce quantum transitions in the molecules, or the molecules may form transient supramolecular complexes with spectral features different from the underlying molecules. Collision-induced absorption and emission is particularly important in dense gases, such as hydrogen and helium clouds found in astronomical systems.
The Morse/Long-range potential (MLR potential) is an interatomic interaction model for the potential energy of a diatomic molecule. Due to the simplicity of the regular Morse potential (it only has three adjustable parameters), it is very limited in its applicability in modern spectroscopy. The MLR potential is a modern version of the Morse potential which has the correct theoretical long-range form of the potential naturally built into it. It has been an important tool for spectroscopists to represent experimental data, verify measurements, and make predictions. It is useful for its extrapolation capability when data for certain regions of the potential are missing, its ability to predict energies with accuracy often better than the most sophisticated ab initio techniques, and its ability to determine precise empirical values for physical parameters such as the dissociation energy, equilibrium bond length, and long-range constants. Cases of particular note include:
Judd–Ofelt theory is a theory in physical chemistry describing the intensity of electron transitions within the 4f shell of rare-earth ions in solids and solutions.
ARTS is a widely used atmospheric radiative transfer simulator for infrared, microwave, and sub-millimeter wavelengths. While the model is developed by a community, core development is done by the University of Hamburg and Chalmers University, with previous participation from Luleå University of Technology and University of Bremen.
Dirubidium is a molecular substance containing two atoms of rubidium found in rubidium vapour. Dirubidium has two active valence electrons. It is studied both in theory and with experiment. The rubidium trimer has also been observed.
Louise Gray Young was an American astronomer and researcher who specialised in molecular spectroscopy. She is best known for her spectroscopic analysis of the planetary atmospheres of Earth, Venus and Mars.