  Understanding the relaxation pathways of photoexcited molecules is essential
to gain atomistic level insight into photochemistry. Herein, we perform a
time-resolved study of ultrafast molecular symmetry breaking via geometric
relaxation (Jahn-Teller distortion) on the methane cation. Attosecond transient
absorption spectroscopy with soft X-rays at the carbon K-edge reveals that the
distortion occurs within $10\pm 2$ femtoseconds after few-femtosecond
strong-field ionization of methane. The distortion activates coherent
oscillations in the scissoring vibrational mode of the symmetry broken cation,
which are detected in the X-ray signal. These oscillations are damped within
$58\pm13$ femtoseconds, as vibrational coherence is lost with the energy
redistributing into lower-frequency vibrational modes. This study completely
reconstructs the molecular relaxation dynamics of this prototypical example and
opens new avenues for exploring complex systems.
