We study the effect of D-instantons on closed string scattering amplitudes in
the two-dimensional type 0B string theory from the worldsheet perspective. We
find that the contribution from a pair of D-instanton and anti-D-instanton to
the closed string reflection amplitude, with a suitable contour prescription
for the integration over the D-instanton moduli space, agrees with the
corresponding leading non-perturbative corrections in the proposed dual matrix
quantum mechanics. This analysis is further extended to thermal observables
defined at finite temperature. The infrared divergence in charged processes is
understood through the measure factor for charged D-instantons, and can be
treated with spacetime dimensional regularization.Comment: 30 pages, 3 figures, 1 tabl