Knowledge Bank

Perturbation allowed transitions and the application of them to the determination of $A0$ and $D0K$ of $CH3D$ were first reported by Olson at this Symposium in 1967 (Abstract $J4$). Such transitions were postulated in $\nu 3$ and $\nu 3+\nu 6$ of $CH3I$ by Maki and $Hexter1$, and subsequently found by Matsuura, Nakagawa, and $Overend.2$ Lovejoy and $Olson3$ reported a few such transitions in the $\nu 1$ and $\nu 4$ bands of $SiH3D$ and Maki, Sams, and $Olson4$ have observed a fairly extensive number of these in the $3\nu 2$ band of $PH3$. A more extensive set of such transitions than in any case known previously has now been found in the $\nu 3$ and $\nu 1$ bands of $AsH3$. These have allowed the determination by combination differences of the ground state rotational constants $B0$, $C0$, $D0J$, $D0JK$, $D0K$, $H0J$, $H0JK$, $H0KJ$, and $H0K$. $\Delta K=3$ combination differences have been obtained for all K pairs from $K=1\to K=2$ up to $K=13\to K=16$. These results will be discussed along with some account of the type of perturbations which have in practice led to perturbation allowed transitions, how one finds such transitions and assigns them, and lastly, where to look for such transitions in some other light symmetric top molecules.