The 2-0, 1-0 and 0-0 bands of the ultraviolet system of PS have been analysed for their rotational structure. It is shown that they involve the transitionC²Σ -X² Π_r(a). TheC²Σ state shows a significant spin doubling.

Fluorescence was excited in theB¹Γ_u −X¹Σ_g⁺ system of Na₂, using the 488 and 514.5 nm radiations from a cw Ar⁺ laser. The fluorescence was monitored through a double monochromator employing photoelectronic detection. In the spectrum resulting from the 488 nm excitation, apart from a large number of fluorescence series, a previously unreported series could be identified. On either side of all the members of the strongest series a large number of collisional satellites were observed and assigned.

A theoretical derivation of closed form expressions for the intensities of all the rotational branches arising out of⁴Σ-⁴Π electronic transition in a diatomic molecule is described. In the present theory the tradition of treating the coupling in the⁴Σ state as belonging to Hund’s case (b) is discarded; instead a full-fledged intermediate coupling treatment which rigorously takes into account the spin-spin and second order spin-orbit effects is presented. Since accurate intermediate coupling treatment of⁴Π, in analytically closed form, is not possible, the⁴Π is first restricted to the extreme coupling scheme Hund’s case (a)(or case (b)); the effect of spin uncoupling (or spin-orbit and spin-spin interactions) is then incorporated through a first order perturbation calculation.

Rovibrational matrix elements of the multiple moments Q_l up to rank 10 and of the linear polarizability of the H₂ molecule in the condensed phase have been computed taking into account the effect of the intermolecular potential. Comparison with gas phase matrix elements shows that the effect of solid state interactions is marginal.