MATRIX-ISOLATED FeO, NiO, AND CoO: GROUND-STATE VIBRATIONAL $FREQUENCIES^{*}$

$^{*}$Work performed under the auspices of the U. S. Department of Energy.Author Institution:The Infrared vibrational spectra of the FeO, NiO, and CoO molecules have been observed in Ar matrices at 14 K. Frequencies for each of the isotopomers $^{54}Fe^{16}O, ^{54}Fe^{18}O, ^{56}Fe^{16}O, ^{56}Fe^{18}O, ^{58}Ni^{16}O, ^{58}Ni^{18}O, ^{60}Ni^{16}O, ^{60}Ni^{18}O, ^{59}Co^{16}O$, and $^{59}Co^{18}O$, were measured.. The derived vibrational constants are: \begin{eqnarray*} \omega_{e} &=& 880.02 \pm 1.2 \; and \; \omega_{e}x_{e} = 3.47 \pm 0.6\; cm^{-1} \; for\; ^{54}Fe^{16}O;\\ \omega_{e} &=& 837.61 \pm 1.1 \; and \; \omega_{e}x_{e} = 5.92 \pm 0.6\; cm^{-1} \; for \; ^{50}Ni^{16}O;\\ and\;\; \omega_{e} &=& 853.75 \pm 1.2 \; and \; \omega_{e}x_{e} = 3.65 \pm 0.6\; cm^{-1} \; for \; ^{59}Co^{16}O.\\ \end{eqnarray*} These results support the assignment of $^{5}\Sigma^{+}$ as the ground state of FeO, $^{3}\Sigma^{-}$ as the ground state of NiO, and $^{4}\Sigma^{-}$ as the ground state of CoO