Electronic spectroscopy and ionization potentials for YbOH and YbOCH3

Abstract

The polyatomic molecules YbOH and ${\mathrm{YbOCH}}_{3}$ have been recognized as being of potential value for spectroscopic experiments that explore charge-parity and time-reversal symmetry violation effects. These measurements require very high precision, which, in turn, will necessitate that the molecules be manipulated at ultracold temperatures. Both YbOH and ${\mathrm{YbOCH}}_{3}$ have electronic transitions that appear suitable for laser cooling ($\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{A}{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Pi}}}_{1/2}\text{\ensuremath{-}}\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{X}{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Sigma}}}^{+}$ and $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{A\phantom{\rule{4pt}{0ex}}}{\phantom{\rule{0.16em}{0ex}}}^{2}{E}_{1/2}\text{\ensuremath{-}}\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{X}{\phantom{\rule{0.16em}{0ex}}}^{2}{A}_{1}$, respectively) but the currently available spectroscopic data are not sufficient to determine the extent to which population leaks may compromise the optical cooling processes. A further complication is that the quantum states of interest for these measurements will need to be selectively populated. The $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{A}\text{--}\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{X}$ band systems of both YbOH and ${\mathrm{YbOCH}}_{3}$ show evidence of vibronic perturbations, such that there are unassigned vibronic features at energies that are just above the origin bands. In the present study we have recorded spectra for the $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{A}$ ${}^{2}{\mathrm{\ensuremath{\Pi}}}_{1/2}\text{\ensuremath{-}}\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{X}{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Sigma}}}^{+}$ transition of jet-cooled YbOD to facilitate the vibronic assignments. In addition, spectra for the $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{B}{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Sigma}}}^{+}\text{\ensuremath{-}}\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{X}{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Sigma}}}^{+}$ transition of YbOH were recorded, establishing the origin band at 20 473.8 $\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1}$. Previously, the reaction of Yb with ${\mathrm{CH}}_{3}\mathrm{OH}$ has been used to generate gas-phase ${\mathrm{YbOCH}}_{3}$. As this reaction also yields YbOH, there have been complications in spectroscopic studies of ${\mathrm{YbOCH}}_{3}$ due to overlap of the $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{A}\text{--}\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{X}$ band systems. To identify specific regions of overlap, resonantly enhanced two-photon ionization spectra were recorded using mass-resolved detection of the $\mathrm{YbO}{\mathrm{H}}^{+}$ and ${\mathrm{YbOCH}}_{3}^{+}$ ions. These data confirmed the overlap of vibronic bands near 17 640 and 17 680 $\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1}$. Two-photon ionization spectroscopy also provided accurate ionization energies (IE), $\mathrm{IE}(\mathrm{YbOH})=45\phantom{\rule{0.16em}{0ex}}788(10)$ and $\mathrm{IE}({\mathrm{YbOCH}}_{3})=45\phantom{\rule{4pt}{0ex}}283(10)\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1}$. The IE for YbOH is relevant to problems encountered in previous attempts to determine the bond-dissociation energy of $\mathrm{YbO}{\mathrm{H}}^{+}$.