Interplanetary shocks are one of the proposed sources of suprathermal ion
populations (i.e., ions with energies of a few times the solar wind energy).
Here, we present results from a series of three-dimensional hybrid simulations
of collisionless shocks in the solar wind. We focus on the influence of the
shock-normal angle, $\theta_{Bn}$, and the shock speed, $V_s$, on producing
protons with energies a few to hundreds of times the thermal energy of the
upstream plasma. The combined effects of $\theta_{Bn}$ and $V_s$ result in
shocks with Alfv\'en Mach numbers in the range 3.0 to 6.0 and fast magnetosonic
Mach numbers in the range 2.5 to 5.0, representing moderate to strong
interplanetary shocks. We find that $\theta_{Bn}$ largely organizes the shape
of proton energy spectra while shock speed controls acceleration efficiency.
All shocks accelerate protons at the shock front but the spectral evolution
depends on $\theta_{Bn}$. Shocks with $\theta_{Bn} \geq 60^\circ$ produce
isolated bursts of suprathermal protons at the shock front while shocks with
$\theta_{Bn} \leq 45^\circ$ create suprathermal beams upstream of the shock.
Downstream proton energy spectra have exponential or smoothed broken power-law
forms when $\theta_{Bn} \geq 45^\circ$, and a single power-law form when
$\theta_{Bn} \leq 30^\circ$. Protons downstream of the strongest shocks have
energies at least 100 times the upstream thermal energy, with $\theta_{Bn} \leq
30^\circ$ shocks producing the highest energy protons and $\theta_{Bn} \geq
60^\circ$ shocks producing the largest number of protons with energies at least
a few times the thermal energy.
