ISO:
Isotopologues are numbered in order of decreasing (terrestrial) abundance.
12 isotopologues are listed for CO2, identified as 1:9 then
'0', 'A', 'B' (ie not strictly
hexadecimal, which would be 'A','B','C'). No other molecule has more
than 7 isotopologues.
gqu, gql:
Although not used by the RFM directly, these are read by the
HITBIN program and converted
to integer indices.
lqu, lql:
Although not used by the RFM directly, these are passed by the
HITBIN program, compressed from
15 to 9 characters, into the .bin
files and, just for CO2, used to identify individual transitions associated
with the internal line-coupling model (MIX
flag).