Density variations over subparsec scales in diffuse molecular gas

We present high-resolution observations of interstellar CN, CH, CH+, Ca I, and Ca II absorption lines toward the multiple star systems HD 206267 and HD 217035. Substantial variations in CN absorption are observed among three sight lines of HD 206267, which are separated by distances of order 10,000 AU; smaller differences are seen for CH, CH+, and Ca I. Gas densities for individual velocity components are inferred from a chemical model, independent of assumptions about cloud shape. While the component densities can differ by factors of 5.0 between adjacent sight lines, the densities are always less than 5000 cm(-3). Calculations show that the derived density contrasts are not sensitive to the temperature or reaction rates used in the chemical model. A large difference in the CH+ profiles (a factor of 2 in column density) is seen in the lower density gas toward HD 217035.