  We introduce high-harmonic sideband spectroscopy (HHSS) and show that it can
be a robust probe of attosecond charge migration (CM) in a halogenated
carbon-chain molecule. We simulate both the CM and harmonic-generation (HHG)
dynamics using ab initio time-dependent density-functional theory. We find that
CM dynamics initiated along the molecular backbone induces sidebands in the HHG
spectrum driven by a delayed laser pulse that is polarized perpendicular to the
molecular axis. Monitoring the spectrum as either the HHG laser frequency or
the relative delay is scanned allows for the extraction of detailed information
about the time-domain characteristics of the CM process.
