THE SUBMILLIMETER-WAVE SPECTRUM OF THE CrH AND CrD $(^{6}\Sigma^{+})$ RADICALS

Author Institution: Department of Chemistry, Department of Astronomy, and Steward Observatory, University of ArizonaThe $N = 0 \to 1$ transition of CrH and the $N = 1 \to 2$ line of CrD in their $^{6}\Sigma^{+}$ ground states have been recorded using submillimeter direct absorption techniques. This study was the first direct measurement of these transitions. These molecules were produced in a discharge plasma of chromium vapor and $H_{2}$ or $D_{2}$ gas. Three fine structure components were measured for each radical, and the proton and deuteron hyperfine splittings were also resolved. Spectroscopic constants were obtained by fitting the data with a Hund's case (b) Hamiltonian including rotation, spin-rotation, spin-spin, magnetic hyperfine, and electric quadrupole interactions. These measurements have resulted in improved spectroscopic constants for both isotopomers. The hyperfine parameters suggest that the bonding in CrH has a nonnegligible covalent character. This molecule may be present in the outer envelope of late-type stars and formed by ion-molecule reactions from neutral or ionized Cr and hydrogen gas. Chromium has a cosmic abundance of $Cr/H = 5 \times 10^{-7}$