Basic definitions
A database of the Internet portal on molecular spectroscopy can contain lists of spectral line parameters from different data sources. The parameters of spectral lines involve frequency, intensity, lower energy state, half-width and some others. As data sources are used as widely known spectroscopic data banks, such as HITRAN[1] and GEISA[2], as original data created by the participants of this project: CDSD[3], S&MPO[4], TheoReTS[5]. If HITRAN and GEISA are a compilation of both calculated and experimental data, the other data sources only contain predicted data. The values of some spectral line parameters depend on temperature and pressure. Therefore, important characteristics of each data source are the reference values of temperature and pressure Tref and Pref, at which the data source contains the values of these parameters.
Portal sites named also as Information systems allow the user to model spectra using a set of spectral functions. Computation of spectral line profiles of gas molecules is based on the line by line method that is summingthe standard line shapes of single absorption lines.Thus, if the device parameters are not set on spectrum simulation, the resulting spectrum is a high-resolution spectrum. If the device parameters are set, the influence of the device is taken into account by using the apparatus function. The resulting spectrum obtained by convolution of the of high-resolution spectral functions by apparatus function of the device is a low-resolution spectrum.
The conversion of the frequency units
As the frequency unit in the portal database is used wavenumber WN in cm-1. To translate wavenumber into other, more familiar to many people units, such as wavelength λ (cm) or frequency ν (Hz), you need to use the following equation:
λ · WN = 1 , so λ = 1/WN (1)
and
λ · ν = с , so ν = с/λ = с · WN , (2)
where с is the speed of light.
Used physical constants
- The Planck constant h = 6.62606957×10−27erg·s ;
- The speed of light c = 2.99792458×1010 cm·s−1 ;
- The Boltzmann constant k = 1.3806488×10−16 erg·K−1 ;
- Second radiation constant c2 = hc/k = 1.4387752 cm·K ;
- The Avogadro constant NA = 6.022140857×1023mol−1 .
References
- L.S. Rothman et al., The HITRAN2012 Molecular Spectroscopic Database // J.Quant. Spectrosc. Radiat. Transfer. 130, 4-50 (2013) (doi:10.1016/j.jqsrt.2013.07.002).
- N. Jacquinet-Husson et al., The 2009 Edition of the GEISA Spectroscopic Database // J. Quant. Spectrosc. Radiat. Transfer., 112, 2395-2445 (2011) (doi:10.1016/j.jqsrt.2011.06.004).
- S.A. Tashkun, V.I. Perevalov, J.-L. Teffo, A.D. Bykov, N.N. Lavrentieva, CDSD-1000, The High-Temperature Carbon Dioxide Spectroscopic Databank // J. Quant. Spectrosc. Radiat. Transfer. 182, 165-196 (2003) (doi:10.1016/S0022-4073(03)00152-3).