  Time-resolved x-ray scattering (TRXS) measures internuclear separations in a
molecule following laser-induced photoexcitation. The molecular dynamics
induced by the excitation laser may lie on one or several bound or dissociative
electronic states. TRXS from these states can be difficult to isolate because
they generally overlap in the angle-resolved x-ray scattering pattern
$I(x,y,{\tau})$, where ${\tau}$ is the pump-probe delay and $x,y$ are the
physical pixel positions. Here we show how standard transform methods can
isolate the dynamics from individual states. We form the temporal Fourier
transform, $\tilde{I}(x,y,{\omega})$$=\int_{-\infty}^{\infty} d\tau
e^{-i\omega\tau} I(x,y,\tau)$. This frequency-resolved x-ray scattering (FRXS)
signal segregates the bound states according to their vibrational frequencies,
${\omega}_i$, and also displays dissociative states along straight lines
${\omega}=vQ$, where the slope $v$ is the rate of increase of the internuclear
distance and $Q$ is the momentum transfer between the incident and scattered
x-ray photon. We derive this relation and use FRXS to extract state-specific
dynamics from experimental TRXS from molecular iodine following a 520 nm pump.
Dynamics observed include one- and two-photon dissociation of the
$^{1}{\Pi}_{u}$ and $^{1}{\Sigma}_{g}^{+}$ excited states, and vibrational wave
packets on the B ($^{3}{\Pi}_{0u}^{+}$)state.
