We present a new, close relation between column densities of OH and CH molecules based on 16 translucent sightlines (six of them new) and confirm the theoretical oscillator strengths of the OH A–X transitions at 3078 and 3082 Å (0.001 05, 0.000 648) and CH B–X transitions at 3886 and 3890 Å (0.003 20, 0.002 10), respectively. We also report no difference between observed and previously modelled abundances of the OH molecule.

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We demonstrate evident Doppler splitting in the profiles of many narrow diffuse interstellar bands (DIBs). Their components are compared with those of atomic and molecular lines of interstellar origin. It is shown that it is likely that the species that shares both wavelength shifts and strength ratios of the Doppler components seen in the DIB profiles is the CH radical. Because of this profile resemblance, it is recommended that CH lines can be used to shift spectra to the rest velocity frame for interstellar features, especially to determine the DIB rest wavelengths on the basis of the CH line at 4300.3132 Å in the spectrum of HD 147889. Our results strongly support a molecular origin of diffuse bands.

Detailed analysis of intensity ratios of unsaturated methylidyne (CH) A--X and B--X bands suggests consistency of the recently published oscillator strengths of A$^{2}\Delta$ -- X$^{2}\Pi$ (0, 0) -- 4300 \AA\ and B$^{2}\Sigma^{-}$ -- X$^{2}\Pi$ (0, 0) -- (3878, 3886 and 3890 \AA) bands (ie. 506, 107, 320 and 213$\times$10$^{-5}$ respectively). This result is based on extremely high S/N ratio spectra of 45 stars, acquired with three high-resolution spectrographs, situated in Chile: ESO LaSilla (HARPS), ESO Paranal (UVES) and Las Campanas (MIKE) and MAESTRO instrument situated in Northern Caucasus (Russia). The calculated methylidyne column densities, obtained using the consistent system of the oscillator strengths toward the observed targets, are given as well. We verify oscillator strengths of the CH+ A-X (0, 0) and (0, 1) bands at 4232 \AA\ and 3957 \AA\ equal to 545 and 342$\times$10$^{-5}$ respectively. We also confirm the lack of correlation between abundances of neutral CH and CH$^{+}$ which the fact demonstrates that they are originated in different environments.

The analysis of radial velocities in the spectra of HD 151932 and HD 152233, performed for the optical lines of interstellar CH and CH+ molecules on one hand, and for the diffuse bands 4964 and 6196 Å on the other hand, suggests that the carrier of the former DIB is spatially related to CH, while the carrier of the latter - to CH+. A further analysis, based on the sample of 106 reddened OB stars, partly confirms this suggestion, showing that the CH column density correlates indeed much better with the equivalent width of the 4964 DIB than with that of the 6196 DIB.