Probing the possibility of a C-12/C-13 abundance gradient from observations of interstellar CH+

High SNR observations of interstellar CH+ have been performed of the reddened, early-type stars HD 24432m, HD 183143, and HD 157038 in an effort to probe the existence of a C-12/C-13 abundance gradient in the Galaxy. The isotope ratios appear to be a true reflection of the isotope ratios in the gas. The measurement results are in good agreement with the local ISM value of 43 + or - 4. Thus, the ISM appears hommogeneous within 1.7 kpc of the sun. The interstellar material in the observed region of the Galaxy has suffered a significant amount of chemical evolution in the past 4.5 billion years. This finding is in disagreement with most of the results derived from radio observations of other molecular species.