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HITRAN Application Programming Interface (HAPI)
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Unphysical gap in CO2 absorption table for isotopologues 1 & 2? #7

Open gpetty opened 5 years ago

gpetty commented 5 years ago

When I plot the molecular cross-sections (scaled by relative abundance) for the first three isotopologues (see attached), absorption for the first two drops out completely between about 1200 and 1420 wavenumbers, leaving the third [(16O)(12C)(18O)] as the dominant isotopologue within that range, despite having an abundance of only 0.4% relative to (12C)(16O)2. Is this a real absorption gap or does it reflect an unphysical gap, either in the HITRAN database itself or in HAPI's transmittal of the data via fetch()? I notice that elsewhere, the three isotopologues show fairly similar behavior.

Each isotopologue line file was obtained with a single fetch statement, so this should not have been a problem with the wavenumber range specified. I tried fetching the data again, with the same result.

I spoke with an IR spectroscopy expert who could not think of a physical reason for such a gap.

CO2_2.pdf

gpetty commented 5 years ago

A perusal of Table 3 in this paper by Tashkun et al. (2015) suggests that there simply was no source for line data in that range for isotopologues 1 & 2, though Toth (1985) supplied measurements for non-symmetric isotopologues (3, 4, 5) only.