  The behavior of a particle in a solvent has been framed using stochastic
dynamics since the early theory of Kramers. A particle in a chemical reaction
reacts slower in a diluted solvent because of the lack of energy transfer via
collisions. The flux-over-population reaction rate constant rises with
increasing density before falling again for very dense solvents. This Kramers
turnover is observed in this paper at intermediate and high temperatures in the
backward reaction of the LiNC $\rightleftharpoons$ LiCN isomerization via
Langevin dynamics and mean first-passage times (MFPTs). It is in good agreement
with the Pollak-Grabert-H\"anggi (PGH) reaction rates at lower temperatures.
Furthermore, we find a square root behavior of the reaction rate at high
temperatures and have made direct comparisons of the methods in the
intermediate- and high- temperature regimes; all suggesting increased ranges in
accuracy of both the PGH and MFPT approaches.
