Knowledge Bank

The Stark spectrum of $PH3$ has been investigated in the far-infrared region using the DCN laser. Several families of absorption lines were observed in both parallel and perpendicular polarizations using electric fields up to 57 000$Vcm$. The multiplet transitions, independently observed with two different DCN laser lines, were assigned as $Jk=6k\leftarrow 5kE,K=1,2,4$, and 5 along with $Jk=63\leftarrow 53A1,2,\leftarrow A1,2$, in the $\nu 2=1$ vibrational state. In addition, several absorption lines belonging to the forbidden zero-field transitions $Jk=63\leftarrow 53A1,2,\leftarrow A1,2$, have been observed for the first time. Accurate zero-field frequencies for all assigned transitions will be presented.