  We present a time-resolved study of the photodissociation dynamics of OCS
after UV-photoexcitation at $\lambda=237$ nm. OCS molecules ($X\,^1\Sigma^+$)
were primarily excited to the $1\,^1\!A''$ and the $2\,^1\!A'$ Renner-Teller
components of the $^1\Sigma^{-}$ and $^1\!\Delta$ states. Dissociation into CO
and S fragments was observed through time-delayed strong-field ionisation and
imaging of the kinetic energy of the resulting CO$^+$ and S$^+$ fragments by
intense $790$ nm laser pulses. Surprisingly, fast oscillations with a period of
$\sim100$ fs were observed in the S$^+$ channel of the UV dissociation. Based
on wavepacket-dynamics simulations coupled with a simple
electrostatic-interaction model, these oscillations do not correspond to the
known highly-excited rotational motion of the leaving CO$(X\,^1\Sigma^+,J\gg0)$
fragments, which has a timescale of $\sim140$ fs. Instead, we suggest to assign
the observed oscillations to the excitation of vibrational wavepackets in the
$2\,^3\!A''$ or $2\,^1\!A''$ states of the molecule that predissociate to form
S$(^3\!P_{J})$ photoproducts.
