Knowledge Bank

Arsine $(AsH3)$ is a pyramidal-type molecule like ammonia. The recent theoretical studies made in connection with the perturbations appearing in the infrared spectra of pyramidal-type molecules prompted the present experimental work. All the four fundamental vibration rotation bands of arsine were studied. Two of these fundamentals (designated as $\nu 1$ and $\nu 2$) occur in the region of 5 microns and the other two (designated as $\nu 2$ and $\nu 4$) are observed in the region of 10 microns. Nearly 2000 rotational lines in the four fundamentals were recorded, measured and analyzed. Based on the experimental data obtained, several molecular parameters of arsine like the moment of inertia, centrifugal distortion constants, etc., were evaluated. The more interesting features are the perturbations observed. The shifts (known as Giant l-type doubling'') of some of the rotational lines $(^{R}R(J,O))$ observed previously for $ammonia^{1}$ and $phosphine^{2}$ in the $\nu_{4}$ band were also seen in the $\nu_{4}$ band of arsine. In addition, for the first time, similar shifts were observed in the $\nu_{4}$ band of arsine although they were much smaller than in the case of the $\nu_{4}$ band. The doubling of lines (known as K-type doubling'') was observed for the first time in some of the rotational lines of the $p3$ band (viz. ) and ). A quantitative correlation was at tempted between the measured splittings of the doublets and the theoretical parameters responsible for their occurrence.