Transition region spectroscopy of dialkali halides: Sodium(2)chloride and sodium(2) + atomic fluorine going to sodium fluoride + sodium

Abstract

Molecular beam chemiluminescence from Na\sb2 + F $\to$ NaF + Na\sp\* was dispersed and measured with a fast spectrograph. Attention was given to emission wavelengths at and around 388.5 and 342.8 nm, which correspond to the electric dipole forbidden atomic transitions Na 4s $\to$ 3s and 3d $\to$ 3s, respectively. It was hoped that the nascent products NaF and Na\sp\* would interact such that these normally dis-allowed transitions could be observed, thereby constituting a direct glimpse of the three atom system late in the reaction event. A small emission peak was observed at the 3d $\to$ 3s transition wavelength, but its weak intensity could be explained by electric quadrupole radiation of the free atom rather than a reaction-induced breaking of dipole selection rules. No structured emission was observed at the 4s $\to$ 3s wavelength, although interference from Na\sb2\sp\* may be obscuring an otherwise observable peak. In a second experiment, two lines of an argon ion laser are crossed with a single Na/NaCl beam in an effort to observe resolved laser-induced fluorescence of the stable molecule Na\sb2Cl. The copious emission from Na\sb2\sp\* precluded any definitive identification of fluorescence from the target molecule. Finally, a detailed description is given of the f/2 spectrograph that was developed in this laboratory. The instrument observes a 100 nm wavelength region simultaneously, images atomic lines to a full-width-half-maximum (fwhm) of 2 nm, has a photocathode quantum efficiency of 3.1% at 800 nm, and exhibits only 36 counts per second dark current