ON THE DETECTION OF INTERSTELLAR HOMONUCLEAR DIATOMIC-MOLECULES

The pure rotational spectrum of homonuclear diatomic molecules in the interstellar medium is strongly forbidden, and no such spectrum has be en detected. In regions of high excitation, vibrational emission may o ccur, as is widely detected in the case of H-2 in interstellar shocks and photon-dominated regions. However, it is of considerable interest to know the abundance of homonuclear diatomics in quiescent regions. W e propose that vibrational emission from homonuclear diatomic molecule s in cold clouds may be detectable, where the excitation is mainly thr ough collisions with non-thermal electrons arising from the cosmic-ray ionization of H-2, As an example, we estimate the intensity of emissi on from N-2 in cold, dark interstellar clouds. We show that such emiss ion is at the limit of detectability with current technology. Other ex citation mechanisms may also contribute and enhance this emission.