If XSCFIL
contains the '#GAS' character string, this is expanded
to the molecule name (lower case, with 'f' numbers for CFCs/HCFCs,
eg 'f12', 'f23')
of any cross-section molecules which do not have an
explicitly assigned .xsc file.
(see Tokens).
Example
*XSC
./examples/aerosol.xsc ! just aerosol.xsc in current directory
../xscfiles/#GAS.xsc ! directory for all other .xsc files