The files 13C1.fit, 13C2.fit, and 13C3.fit are slightly reduced files 
generated by spfit for the corresponding isotopolog. The files are text files.
The complete files as well as line, parameter, and other files are available under

https://cdms.astro.uni-koeln.de/classic/predictions/daten/CH3CCH/13C/

The names refer to the position of the 13C atom in the respective isotopolog. 
In the usual CDMS/JPL notation, the substituted atom is indicated by the mass 
shown after the atom between dashes.

13C1: CH3CC-13-H
13C2: CH3C-13-CH
13C3: C-13-H3CCH

The first line is a title line; the second line gives basic informations on the fit;
the third non-empty line is the header for the line list:
# indicates the number of the line, 2 upper and 2 lower state quanta are next, 
followed by observed frequency, calculated frequency, residual obs. - calc., and 
the experimental uncertainty. All values are in units of megahertz.

The lines are grouped according to the sources, separated by empty lines.
The first group (2 lines) are from Tranbarulo and Gordy (Ref. 42),
The second and fourth group are from Dubrulle et al. (Ref. 45),
The third and the fifth group are from this work.

A list of parameter codes, parameter names, and parameter values with uncertainties in units 
of megahertz follow. Parameter values with uncertainty of 0 were kept fixed in the fit. 
The fits are converged as indicated by the zero changes in the parameter values. 

The correlation coefficients follow after microwave average deviation, microwave rms, 
and rms error.