The Ohio State University Data contained in Splatalogue

Below are the notes sent from Ivan Medvedev and Sara Fortman from The Ohio State University regarding the OSU data contained in Splatalogue.:

The data that are present in Splatalogue are the preliminary ethyl cyanide (CH3CH2CN) data table containing lower state energy, line strength (D2) and line frequency (MHz). The table contains ~3000 strongest lines, with an intensity cut off of ~300/1 of the strongest line. With this signal-to-noise, detection of the 13C isotopologues is marginal.

The OSU group also reports the temperature independent line strength. If a user of the data then wishes to determine the temperature dependent absorption coefficient, it can be calculated using the standard equation with the partition function taken from the JPL database. This will give the correct relative intensity patterns, but will not account for the contribution from the vibrational partition function, which will have to be calculated one way or the other to have correct absolute intensity. Users can probably get away with harmonic approximation, although coupling of the vibration and torsion will require more sophisticated analysis.


Experimental Intensity Calibrated Spectra as a Function of Temperature

The development of experimental intensity calibrated spectra as a function of temperature has been described in the Astrophysical Journal.[1,2] Here we provide a link to these data that mirrors that held in its electronic archives and provide an introduction to their use.

Briefly, the links below are to pairs of coefficients (ijμ2 and Ẽ̃) for each spectral data point (typically several million pairs) in a spectral interval. At line centers, these coefficients correspond to the linestrength and lower state energy of the line, but off of line center and in blends these parameters include information about lineshape as well. ijμ2 is reported in units of D2 (Debye squared) and in units of cm-1. The absorbance scaled by the nL/Q parameter at an arbitrary temperature is given by


,

with n the number density (/cm3), L (cm) the column length, and Q the partition function. Q has the same meaning as in the JPL and Cologne databases. The constants are given by


,

with M the molecular weight in amu, T temperature in K, and ν frequency in MHz. Additional details are provided in the aforementioned references.


[link on point-by-point reference page - coming soon!]: Ethyl Cyanide


[on linked page - coming soon!]:

210 – 270 GHz: 2.4 million spectral points, starting at 210 000.000 MHz, in increments of 0.025 MHz. At 300 K this spectrum contains more than 9500 features with a S/N greater than two, belonging to approximately 40 vibrational states. Some of the lines in this analysis are also due to the 13C isotopic species. [3] [links to files]


570 – 648 GHz: 1.2 million spectral points, starting at 570 000.000 MHz, in increments of 0.065 MHz. At 300 K this spectrum contains more than 11000 features with a S/N greater than two, belonging to approximately 40 vibrational states. Some of the lines in this analysis are also due to the 13C isotopic species.[2] [links to files]


[1] I.R. Medvedev, F.C. De Lucia, An experimental approach to the prediction of complete millimeter and submillimeter spectra at astrophysical temperatures: Applications to confusion-limited astrophysical observations, Ap. J. 656 (2007) 621-28.

[2] S.M. Fortman, I.R. Medvedv, C. F. Neese, F.C. De Lucia, A new approach to astrophysical spectra: The complete experimental spectrum of ethyl cyanide (CH3CH2CN) between 570 and 645 GHz, Ap.J. 714 (2010) 476-86.


[3} S.M. Fortman, I.R. Medvedv, C. F. Neese, F.C. De Lucia, The complete experimental spectrum of ethyl cyanide (CH3CH2CN) between 210 and 270 GHz, in submission process.