OF the diatomic emitters of band spectra, few have been more extensively studied than the 14-electron molecules N2 and CO, which are responsible for many observed band systems and, unlike most emitters, are well known as stable molecules rather than as intermediate products in chemical reactions or equilibrium products at high temperatures. Emitters which are chemically or spectroscopically analogous to these two have, as would be expected, also received considerable attention, the best known examples being the 30-eleetron molecule P2 and the 22-electron molecules SiO and CSTo the latter category the PN molecule becomes an interesting addition as the result of the recent discovery and analysis, by J. Curry, L. Herzberg and G. Herzberg, of an ultra-violet band system which is produced by an electrical discharge through a mixture of phosphorus vapour and pure nitrogen. With a heavy discharge (about 6000 v. and £ amp.) in a water-cooled tube, this PN system has been photographed in the first and second orders of a 3-m. grating, and both the vibrational and rotational structures analysed.
J. Chem. Phys., 1, 749; 1933 (preliminary report). Z. Phys., 86, 348; 1933.
Particulars of these band-systems and of the notation used in the PN paper and in the present article are given in the writer's "Report on Band Spectra of Diatomic Molecules" (Phys. Soc., 1932). The more recent analysis of SiO bands is by Saper (Phys. Rev., 42, 498; 1932) and that of CS bands is by Crawford and Shurcliff (Phys. Rev., 43, 766; 1933).
G. Herzberg, Ann. Phys., 15, 677; 1932.
Lozier, Phys. Rev., 44, 575; 1933.
Lochte-Holtgreven and van der Vleugel, Z. Phys., 70, 188; 1931.