[en] The sudden approximation is used to compute integral and differential cross sections for H⁺+H₂(v=0) →H⁺+H₂(v'=1--4) using an ab initio DIMZO (diatomics-in-molecules, zero overlap) potential-energy surface. Good agreement was obtained above 100 eV with calculations of Gentry and Giese using the DECENT approximation. Agreement with the experiments of Hererro and Doering seems fair if their data are properly analyzed. Several useful numerical approximations are developed and tested. These result in savings of several orders of magnitude in computation time