SIMBAD references

We have searched for molecular CH₂ in the interstellar gas in the line of sight to HD 154368 and ζ Oph to constrain further the gas-phase chemistry of carbon-bearing molecules in the cool, translucent clouds toward these stars. We report tentative detection of CH₂ in the interstellar spectra of both stars. In ζ Oph, slight depressions in the stellar continuum are seen near 1410.1 and 1415.8 Å corresponding to band structure in CH₂, while in HD 154368 a single, narrow feature is found at 1410 Å that may be due to CH₂. Assuming that these features are produced by CH₂, the column densities of CH₂ toward HD 154368 and ζ Oph are (5.9±3.1)x10¹³ cm^–2 (W_λ1410.1=5.2 mÅ) and (3.3±1.9)x10¹³ cm^–2 (W_λ1415.8=29 mÅ), respectively. Although the oscillator strengths for the relevant electronic transitions are somewhat problematic, our deduced column densities are within a factor of 2-5 of those predicted by the model chemistry. These observations may represent the first detection of CH₂ interstellar absorption in any astronomical object. Additional theoretical estimates and laboratory measurements of relevant oscillator strengths are needed to provide more accurate estimates of CH₂ column densities and stronger constraints on the carbon chemistry in these interstellar molecular clouds.