  We examine the effects that dynamical instability has on shaping the orbital
properties of exoplanetary systems. Using N-body simulations of non-EMS (Equal
Mutual Separation), multi-planet systems we find that the lower limit of the
instability timescale $t$ is determined by the minimal mutual separation
$K_{\rm min}$ in units of the mutual Hill radius. Planetary systems showing
instability generally include planet pairs with period ratio $<1.33$. Our final
period ratio distribution of all adjacent planet pairs shows dip-peak
structures near first-order mean motion resonances similar to those observed in
the \kepler\ planetary data. Then we compare the probability density function
(PDF) of the de-biased \kepler\ period ratios with those in our simulations and
find a lack of planet pairs with period ratio $> 2.1$ in the
observations---possibly caused either by inward migration before the
dissipation of the disk or by planet pairs not forming with period ratios $>
2.1$ with the same frequency they do with smaller period ratios. By comparing
the PDF of the period ratio between simulation and observation, we obtain an
upper limit of 0.03 on the scale parameter of the Rayleigh distributed
eccentricities when the gas disk dissipated. Finally, our results suggest that
a viable definition for a `packed' or `compact' planetary system be one that
has at least one planet pair with a period ratio less than 1.33. This criterion
would imply that 4\% of the \kepler\ systems (or 6\% of the systems with more
than two planets) are compact.
