Knowledge Bank

Using a molecular beam electric resonance spectrometer we measured the $J=0,\Delta J=0$ spectra of $Na35Cl(v=0,1,2,3)$ and $Na37Cl(v=0,1)$ at 220 and 300 V/cm. Only single lines and lines composed of two components of equal intensity were used to determine the dipole moments and hyperfine constants. Recently, Cederberg, Miller and Zorn (Bull. of Amer. Phys. Soc. 13, 20 (1968)) and Melendres (Thesis Berkeley, 1968) measured the same transitions using the same technique. The results of both these investigations for the quadrupole coupling constants of the v = 0 level of $Na35Cl$ agree well. The present investigation of this molecule in our laboratory resulted, however, in values which differ by approximately 80 kc/s from above mentioned values, while Cederberg et. al. stated their errors to be 3 kc/s. Our errors in the quadrupole coupling constants for the v = 1,2 levels of $Na35Cl$ and of the v = 0,1 levels of $Na37Cl$ are about a factor of 2 smaller than for the v = 0 level of $Na35Cl$. The reason for this is that in the last case the constants are approximately equal and strongly correlated in the calculation of the spectra: changing both quadrupole constants by $\Delta$ and $-\Delta$ respectively does not change the calculated spectra. The same remark can be made with respect to the weak field spectra measured by Cederberg et. al.: these authors determined the sum of the quadrupole constants much more accurately than the difference. Their value for half of the sum ($-5656.77\pm .1$ kc/s) agrees very well with our value ($-5657.15\pm .5$ kc/s), half of their difference ($100\pm 3$ kc/s), however, does not correspond to our value ($14.5\pm 4$ kc/s). Our values for the dipole moments are all about $1\times 10-4$ smaller than Melendres' values. Comparison of our results with Matcha's calculations for NaCl (J. Chem. Phys. 48, 335 (1968)) shows agreement of the dipole moments within about 2%, and yields quadrupole moments for the Na- and Cl-nuclei that are roughly 10% smaller and 30% larger than the values obtained by atomic beam measurements. The next tables show our results and present for comparison the most precise results up till now in the literature. [FIGURE]