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Question About Information Provided in the Lovas Spectral Line List

-- Haider | February 9, 2020

Artist impression of a supermassive black hole

Question:

Dear Jeff,

This is regarding the detection of new molecules in interstellar medium. Suppose we theoretically calculate the microwave spectrum of any molecules and match it with the available frequencies on the site “https://physics.nist.gov/cgi-bin/micro/table5/start.pl”. How much difference is considerable. Now I take an example, The frequency “31092.1-MHz ” is undefined. However, “31093.029 (8)-M.Hz” is defined for C8H.
1- How we can take such a small difference in account.
2-The value in parenthesis indicate what, is it standard deviation (+, – 8).
3- If we have experimental value of rotational constant and calculate the value of 2B then how much match should be there in this value and the value observed by the telescope.

with regards

Haider Abbas
Department of Physics
Manav Rachna University
Faridabad, Haryana, India

-- Haider

Answer:

The uncertainties listed in any laboratory-measured frequencies quoted in the Lovas spectral line list you refer to are 1-sigma uncertainties in the last digit(s) of the frequency listed. In order to find out what the uncertainty in the frequency is for an astronomically-measured frequency, such as the unidentified spectral line you list, you need to refer to the reference for the astronomical measurement. For the example you provided, as long as the unidentified spectral line has been measured to an accuracy that is better than about 1 MHz, then it is safe to say that it is not the nearby transition from the C8H molecule.

-- Jeff Mangum

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