  X-ray Transient Absorption Spectroscopy near the carbon K-edge (1s, $\sim$
285 eV) and chlorine L$_{2,3}$ edges (2p, $\sim$ 200 eV) is used to study the
nuclear dynamics of CCl$_4$ vibrationally activated by impulsive stimulated
Raman scattering with a few-cycle 800 nm pump pulse. The totally symmetric
stretching mode leads to a strong response in the inner-shell spectra, with the
concerted elongation (contraction) in bond lengths leading to a red (blue)
shift in the X-ray absorption energies associated with core-to-antibonding
excitations. The relative slopes of the potential energy surfaces associated
with the relevant core-excited states along the symmetric stretching mode are
experimentally measured and compared to results from restricted open-shell
Kohn-Sham calculations. A combination of experiment and theory indicates that
the slope of the core-excited potential energy surface vs totally symmetric
bond elongation is $-11.1 \pm 0.8$ eV/{\AA} for the Cl 2p$\to7a_1^*$
excitation, $-9.0\pm0.6$ eV/{\AA} for the Cl 2p$\to8t_2^*$ excitation and
$-5.2\pm 0.4$ eV/{\AA} for the C 1s$\to8t_2^*$ excitation, to 95% confidence.
The much larger slopes for the Cl 2p excitations compared to the C 1s state are
attributed to greater contributions from Cl to the $7a_1^*$ or $8t_2^*$
antibonding orbitals to which the inner-shell electrons are being excited. No
net displacement of the center of the vibrational wavefunction along the other
vibrational modes is induced by the pump pulse, leading to absence of transient
signal. The results highlight the ability of X-ray Transient Absorption
Spectroscopy to reveal nuclear dynamics involving tiny ($<0.01$ {\AA}) atomic
displacements and also provide direct measurement of forces on core-excited
potential energy surfaces.
