Subject photoionization cross sections

In the current study and similar studies reported by Schumacher and coworkers, the ratio of sodium atoms to sodium trlmers is thought to be between 10 and 40 to one as a function of experimental conditions (a more exact estimate will require more certain measurement of the cross sections for electron impact and/or photoionization cross sections). The difference in monomer and trimer abundance can easily be overcome by the density of effective states in Nas which significantly exceeds those in atomic sodium. Because of the Increased density of states, it would not be surprising if the cross section for Na2 -Na3 energy transfer far exceeded that for Na2 -Na. The energy transfer phenomena is currently the subject of further investigation in our laboratory. 

In interstellar regions subjected to fast shocks, the radiation field may have a very high intensity at 1215.6 A, because of recombination and collisional excitation of atomic hydrogen leading to Lyman a radiation (Hollenbach and McKee 1979 Neufeld and Dalgarno 1988). It is thus important to know whether a molecule has a photodissociation or photoionization channel at this wavelength. Molecules such as Hj, CO and Nj cannot be destroyed by Lyman a radiation, whereas other species like OH and H2O have cross sections of a few times 10 cm at 1215.6 A and are thus easily dissociated. Another strong peak in the radiation field in shocks is provided by the C III resonance line at 977 A. 

---