Vibrational analysis of the (B ² П→X ² П) system of NS

Abstract

A few red degraded bands attributable to NS have been reported earlier byFowler andBarker, Dressler andBarrow et al, and they occur in the same region (2300 to 2700 Å) as the bands of the known systems (C ² ∑ ⁺−X ² П) and (A ² Δ−X ² П). Measurements made on the heads of some of these weak bands ledBarrow et al. to believe that these bands may form a system analogous to theβ-system of NO and be due to a² П-² П transition. The spectrum of NS has now been studied in a little more detail by means of an uncondensed discharge through dry nitrogen and sulphur vapour in the presence of argon and thirty three bands belonging to this system have been recorded in the region 2280 to 2760 Å. It has been found possible to represent the band heads by means of the equation

$$^v {\text{head}} {\text{ = }} \left. {_{43182 \cdot 5}^{{\text{43311}} \cdot {\text{5}}} } \right\}_{ - [1219 \cdot 20(v'' + \tfrac{1}{2}) - 7 \cdot 48(v'' + \tfrac{1}{2})^2 ].}^{ + [761 \cdot 04(v' + \tfrac{1}{2}) - 5 \cdot 10(v' + \tfrac{1}{2})^2 ]}$$

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Taking the lower state doublet interval as 223 cm⁻¹, it is shown that the separation in the upper state is 94 cm⁻¹. The ratio of the force constants in the upper and the ground states is found to be 0·39 and is nearly the same as that in theβ-system of NO (0·30). The present vibrational analysis therefore supports the view that these new red degraded bands of NS arise from a (B ² П→X ² П) transition and the observed intensity distribution in the form of a wide parabola is also in qualitative agreement with what is expected from the moderately largeΔ r _e (∼0·12Å) value.