HCOOH interstellar

CH3I (methyl iodide) principal axes, 103 If rotation, 113 CH2NH (methanimine) interstellar, 120 Cr203 (chromium trioxide) in alexandrite laser, 347ff in ruby laser, 346ff HC3N (cyanoacetylene) interstellar, 120 HCOOH (formic acid) interstellar, 120 NH2CN (cyanamide) interstellar, 120... 

The presence in interstellar space of many molecular species has been shown by observation of microwave spectral emission lines. Examples include H20, NH3, H2CO, HCN, CH3OH, HCOOH, HCCCN, CO, HCONH2, C2H5OH, and OH. See P. M. Solomon, Physics Today, March 1973, p. 32. 

HOC+, the metastable isomer to the well-known HCO+ molecule, has probably been detected in the galactic centre source Sgr B2 (Woods et al. 1983). This identification rests on only the J = 1 - 0 transition, which has been measured in the laboratory by Gudeman and Woods (1982). Since this line lies in the galactic centre near several rotational transitions of HCOOH, there remains some doubt as to the proper identification. An unambiguous interstellar identification of HOC + would therefore have to await the detection of higher rotational transitions, which have been measured in the laboratory by Blake et al. (1983), or isotopically substituted species. In addition, the HCO+/HCO+ abundance ratio of 330 obtained from the observation is at odds witt theoretical determinations (De Frees et al. 1984 Jarrold et al. 1986). 

Because of the high precision with which the frequencies of the interstellar lines can be measured (better than 1 part in 10s) there remains usually little doubt about the positive identification of the molecular species, despite the fact that only a few transitions out of the whole rotational spectrum of any one given molecule have been observed to date in the radio frequency range. Confirmation is obtained from observations of other rotational transitions, or from the detection of possible fine-structure components, or from observations of corresponding transitions of isotopically substituted species. However, some uncertainty still remains in the identification of formic acid, HCOOH, whose 1 io-ln transition is located in between two 18OH resonances. An independent search for the l0i — 0Oo transition for formic acid was negative (Snyder and Buhl, 1972). Similarly the identification of H2S and H20 still rests on only one observed interstellar radio transition and awaits further confirmation by the detection of other transitions. 

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