  Rate coefficients for rotational transitions in H_2 induced by H_2 impact are
presented. Extensive quantum mechanical coupled-channel calculations based on a
recently published (H_2)_2 potential energy surface were performed. The
potential energy surface used here is presumed to be more reliable than
surfaces used in previous work. Rotational transition cross sections with
initial levels J <= 8 were computed for collision energies ranging between
0.0001 and 2.5 eV, and the corresponding rate coefficients were calculated for
the temperature range 2 < T <10,000 K. In general, agreement with earlier
calculations, which were limited to 100-6000 K, is good though discrepancies
are found at the lowest and highest temperatures. Low-density-limit cooling
functions due to para- and ortho-H_2 collisions are obtained from the
collisional rate coefficients. Implications of the new results for non-thermal
H_2 rotational distributions in molecular regions are also investigated.
