Structure and dynamics of HD${}^{+}$ in the vicinity of the H${}^{+}$ + D and D${}^{+}$ + H dissociation thresholds: Feshbach resonances and the role of g/u-symmetry breaking

We report on the measurement and analysis of photoionisation, mass-analysed-threshold-ionisation and pulsed-field-ionisation zero-kinetic-energy photoelectron spectra of HD in the vicinity of the dissociative-ionisation thresholds H${}^{+}$ + D(1s) + e${}^{-}$ and H(1s) + D${}^{+}$ + e${}^{-}$. The spectra were recorded via the $v=11$-13 vibrational levels of the $\bar{\mathrm{H}}$ and $\bar{\mathrm{B}}$ outer wells of the H$\bar{\rm H}$$^1\Sigma_g^+$andB$^{\prime\prime}\bar{\rm B}$$^1\Sigma_u^+$ states and provide information on the weakly bound levels of the X${}^{+}$ ${}^2{\mathrm{\Sigma }}_g^{+}$ ground state of HD${}^{+}$ with vibrational quantum numbers $v^{+}=16$-21 and rotational angular-momentum quantum numbers $N^{+}=0$-10. The spectra also reveal for the first time shape and Feshbach resonances of HD${}^{+}$ located energetically above the H${}^{+}$ + D(1s) dissociation limit. The structure and dissociation dynamics of the $\bar{\mathrm{H}}$ and $\bar{\mathrm{B}}$ states of HD and of the X${}^{+}$ ${}^2{\mathrm{\Sigma }}_g^{+}$ and A${}^{+}$ ${}^2{\mathrm{\Sigma }}_u^{+}$ states of HD${}^{+}$ near the dissociation thresholds are strongly influenced by the g/u-symmetry breaking caused by the nuclear-mass asymmetry.