H2CO interstellar

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. 

Formaldehyde has been detected recently in the interstellar medium by microwave spectroscopy (593), It is a combustion product of hydrocarbons. The photolysis of H2CO by sunlight in the troposphere may produce H02 radicals by reactions such as... 

Molecular astronomy of carbon molecules is very rich. Of about 120 known interstellar molecules more than three-quarters contain carbon atoms diatomic molecules include CO, CN, C2, CH, CH+, CN+, and CO+ polyatomic include CH2, CH4, C2H2j CH OH, CH3CH2OH, H2CO and HNC large complex unsaturated radicals and polycyclic aromatic hydrocarbons are also detected. These all play a role in the thermochemistry of interstellar clouds. The 2.6-millimeter line of CO diagnoses density and temperature in molecular clouds, as do other molecules. 

To date 150 species have been detected in the interstellar space.1 Among these species only a handful of molecules have been spatially resolved in disks CO (and the isotopomers 13CO and C180), CN, HCN, DCN, HNC, H2CO, C2H, CS, HCO+, H13CO+, DCO+, and N2H+ (Koemer Sargent 1995 Dutrey etal. 1997 ... 

However, the detection of radio spectral lines in the frequency range of about 22 to 23 GHz from the polyatomic molecules NH3 and H20 (in 1968 and 1969) by Cheung et al. and the discovery of the organic molecule H2CO (in 1969) by Snyder et al. marked the beginning of a long series of discoveries. From these and all subsequent discoveries it became evident that dense and cool condensations of the interstellar matter are particularly rich in molecules. 

Fig. 20 shows the observed interstellar molecular lines of various isotopic species of formaldehyde, H2CO, as detected by Gardner et al., 1971. This particular line, the lowest asymmetry-doublet transition 110 — lu, is seen in absorption in the continuum radiation of the strong radio source Sgr B2, which is located behind the molecular gas cloud. Frequency is plotted along the abscissa and the ordinate is intensity, expressed in the ratio of line-to-continuum antenna temperatures. For all three formaldehyde isotopes the continuum temperature is Tc T >b Tex- This is the case because the formaldehyde molecules are in approximate equilibrium with the microwave background... 

Another striking example of non-equilibrium conditions in interstellar space is the observation of the anomalous absorption of H2CO in various K-type levels. The X6 cm rotational transition 110 — In has been found in absorption in many galactic continuum sources (i.e. HII regions and supernovae remnants), even when their continuum temperatures are only a few degrees, indicating that the excitation temperature of the 6 cm line must be very low,... 

The very existence of molecules in interstellar space has provided considerable new insight into the interstellar chemistry of our Galaxy. By providing birth and certainly shelter to molecules like HCN, H20, NH3 and H2CO, known to be important in reactions which synthesize amino acids, the interstellar environment is not nearly as hostile as had originally been assumed. 

Figure 4. The photochemical evolution of an H20 CHs0H NHs C0 CsHg (100 50 10 10 10) interstellar ice analog as traced by infrared spectra measured at 10 K. The spectra were taken before (a) and after 1 hour (b) and 6 hours (c) of UV irradiation. Note the ready formation of CO2, H2CO, CH4, and XCN (now known to be OCN) at the expense of CH3OH. Figure adaptedfrom reference 14.

Lastly, a comment is in order regarding the other abundant interstellar ice components CO2, OCN (XCN), CH4, and H2CO listed in Table I. We are not concerned with their absence in the starting mixture because, as explained above (e.g. Figure 4) they are readily produced upon photolysis at concentrations consistent with the observations. As these are produced at the expense of... 

Mengel, M. and De Lucia, E.C., Helium and hydrogen induced rotational relaxation of H2CO observed at temperatures of the interstellar medium, Aftrcpfeys. 7., 543,271-274, 2000. 

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