SPECTROSCOPIC EVIDENCE OF THE B2 MOLECULE AND DETERMINATION OF ITS STRUCTURE

Abstract

In a discharge in helium with a trace of boron trichloride a new band system is found. The observation of isotope bands and in particular of an intensity alternation in the fine structure shows that the system is due to the diatomic boron molecule, B2. The B211 band heads are represented by the formula[Formula: see text]The bands consist of single R and P branches. The fine structure analysis yields the following rotational constants: Be′ = 1.160, Be″ = 1.212, α′ = 0.011 and α″ = 0.014 cm.−1. From these the internuclear distances re′ = 1.625 and re″ = 1.590Å are obtained. It is shown that in all probability the system represents a 3Σu− − 3Σ0−transition, the lower state being the ground state.From the intensity alternation in the B211 bands, the spin of the B11 nuclei is found to be 5/2. This value is in disagreement with recent theoretical predictions based on the Hartree as well as on the α-particle model of the nucleus.Finally, a comparison with the other homonuclear diatomic molecules of the second period of the periodic system is made as well as a comparison of B2 and C2 with B2H6 and C2H6.