  Although supercontinuum sources are readily available for the visible and
near infrared, and recently also for the mid-IR, many areas of biology,
chemistry and physics would benefit greatly from the availability of compact,
stable and spectrally bright deep ultraviolet (DUV) and vacuum ultraviolet
(VUV) supercontinuum sources. Such sources have however not yet been developed.
Here we report the generation of a bright supercontinuum, spanning more than
three octaves from 124 nm to beyond 1200 nm, in hydrogen-filled kagom\'e-style
hollow-core photonic crystal fiber (kagom\'e-PCF). Few-{\mu}J, 30 fs pump
pulses at wavelength 805 nm are launched into the fiber, where they undergo
self-compression via the Raman-enhanced Kerr effect. Modeling indicates that
before reaching a minimum sub-cycle pulse duration of ~1 fs, much less than one
period of molecular vibration (8 fs), nonlinear reshaping of the pulse
envelope, accentuated by self-steepening and shock formation, creates an
ultrashort feature that causes impulsive excitation of long-lived coherent
molecular vibrations. These phase-modulate a strong VUV dispersive wave (at 182
nm or 6.8 eV) on the trailing edge of the pulse, further broadening the
spectrum into the VUV. The results also show for the first time that
kagom\'e-PCF guides well in the VUV.
