Knowledge Bank

Previously several molecules have been studied in the centimeter region of the spectrum with molecular beam masers. Notably, $NH3,NH2D,HDO,HDS,CH2O,CHDO$, and $D2O1-4$ For each molecule extensive hyperfine structure was revealed that had previously been obscured by Doppler broadening. For reasons of intensity, state selection, and frequency accessibility all of these masers have operated on either inversion or K-type doublet levels that are relatively isolated from other levels. Two millimeter masers have been operated previously at 72 $kMc5$ and $88kMc5$, but, to the best of our knowledge, no spectroscopic data has been reported. We have extended high resolution molecular beam maser spectroscopy into the millimeter and submillimeter region and applied it to the $J=1\to 0$ and $J=2\to 1$ rotational transitions of HCN and DCN at 88 kMc, 177 kMc, 72 kMc, and 144 kMc, respectively. Deuterium coupling in DCN has been widely resolved and (eqQ)D=194.4 kc and $CD=-0.6$ kc determined. The nitrogen coupling has also been measured with improved accuracy for HCN and DCN: $(eqQ)N=-4709.1kc,-4703.0kc;CN=10.4kc,8.4kc$, respectively. Significant improvements in their rotational constants have also been made: $HCN,B0=44,315,975.7kc$ and $DJ=87.24kc;DCN,BO=36,207,462.7kc$ and $DJ=57.83kc$. A preliminary measurement on the $I10\to I01$ transition of $D2O$ at 316 kMc $(\lambda =0.95mm)$ has also been made. This work represents the first successful operation of a molecular beam maser in the submillimeter region---and, so far as we are aware, the $B0$ and $DJ$ for HCN and DCN are the first such molecular rotational constants to be evaluated with a molecular beam maser. We believe these to be the most accurate rotational constants ever measured. This work is supported by the U.S. Air Force Office of Scientific Research, Grant AF-AFOSR-66-0493A.