Following the Swift X-ray observations of the 2006 outburst of the recurrent nova RS Ophiuchi , we developed hydrodynamical models of mass ejection from which the forward shock velocities were used to estimate the ejecta mass and velocity . In order to further constrain our model parameters , here we present synthetic X-ray spectra from our hydrodynamical calculations which we compare to the Swift data . An extensive set of simulations was carried out to find a model which best fits the spectra up to 100 days after outburst . We find a good fit at high energies but require additional absorption to match the low energy emission . We estimate the ejecta mass to be in the range ( 2 - 5 ) \times 10 ^ { -7 } ~ { } { { M } _ { \odot } } and the ejection velocity to be greater than 6000 { ~ { } { km s } ^ { -1 } } ( and probably closer to 10 , 000 { ~ { } { km s } ^ { -1 } } ) . We also find that estimates of shock velocity derived from gas temperatures via standard model fits to the X-ray spectra are much lower than the true shock velocities .