  A time-dependent bond-hardening process is discovered in a polyatomic
molecule (tetramethyl silane, TMS) using few-cycle pulses of intense 800 nm
light. In conventional mass spectrometry, symmetrical molecules like TMS do not
exhibit a prominent molecular ion (TMS$^+$) as unimolecular dissociation into
[Si(CH$_3$)$_3]^+$ proceeds very fast. Under strong field and few-cycle
conditions, this dissociation channel is defeated by time-dependent
bond-hardening: a field-induced potential well is created in the TMS$^+$
potential energy curve that effectively traps a wavepacket. The time-dependence
of this bond hardening process is verified using longer-duration ($\geq$ 100
fs) pulses; the relatively "slower" fall-off of optical field in such pulses
allows the initially trapped wavepacket to leak out, thereby rendering TMS$^+$
unstable once again. Our results are significant as they demonstrate (i)
optical generation of polyatomic ions that are normally inaccessible and (ii)
optical control of dynamics in strong fields, with distinct advantages over
weak-field control scenarios that demand a narrow bandwidth appropriate for a
specified transition.
