  We consider transitions of electron holes (vacancies in otherwise filled
shells of atomic systems) in multiply-charged ions that, due to level-crossing
of the holes, have frequencies within the range of optical atomic clocks.
Strong E1 transitions provide new options for laser-cooling and trapping, while
narrow transitions can be used for high-precision spectroscopy and tests of
fundamental physics. We show that hole transitions can have extremely high
sensitivity to alpha-variation due to large relativistic corrections, and
propose candidate transitions that have much larger alpha-sensitivities than
any previously seen in atomic systems.
