  Recent optical spectra of post-AGB stars show the presence of C2, CN, and CH+
originating in the circumstellar shell. We present here new, higher resolution
spectra which provide constraints on the physical parameters and information on
the line profiles. An empirical curve of growth for the C2 Phillips and CN Red
system lines in the spectrum of HD 56126 yields b = 0.50 (+0.59, -0.23) km/s.
CH+ (0,0) emission lines in the spectrum of the Red Rectangle have been
resolved with a FWHM approx 8.5 pm 0.8 km/s. The circumstellar CN lines of IRAS
08005--2356 are resolved into two separate components with a velocity
separation of Delta v = 5.7 pm 2.0 km/s. The line profiles of CN of HD 235858
have not been resolved.
