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The band system of NSF with origin at 25 487 cm-1 (3923 Å) has been photographed in absorption at high dispersion. Rotational analyses have been carried out for four bands including the 0-0 band. The bands have type-c polarization, corresponding to an electronic transition 1A''-1A'. The geometry for the excited state is r0(NS) = 1·56 Å, r0(SF) = 1·63 Å and ∠ NSF = 101·6°, the principal changes on excitation being an increase in NS bond length of 0·11 Å and a decrease in valence angle of 15·3°. This change in angle is contrasted with those for the lowest excited states of other molecules with 18 valence electrons.

It is shown from gas phase band intensity measurements that the ã - X system of CS2 is vibronically induced with a transition moment proportional to the second power of the bending normal coordinate of the linear ground state. Hence it is deduced that the ã, 3A2 state of bent CS2 is derived from the 2u component of a 3Δu state of linear CS2. This orbital nature of the ã state is also consistent with the observed Zeeman effect.