The reaction of hydroxy peroxy radicals (RO2) with NO represents one of the most crucial tropospheric processes, leading to terrestrial ozone formation or NO, removal and chain termination. We investigate the formation of hydroxy peroxy nitrites (ROONO) and nitrates (RONO2) from the OH-isoprene reactions using DFT and ab initio theories and variational RRKM/master equation (vRRKM/ME) formalism. The binding energies of ROONO from NO addition to RO2 are determined to be in the range of 20-22 kcal mol(-1), and the bond dissociation energies of ROONO to form an alkoxy radical (RO) and NO2 range from 6 to 9 kcal mol(-1). Isomerization of ROONO to RONO2 is exothermic by 22-28 kcal mol(-1). The entrance and exit channels of the RO2-NO reaction are found to be barrierless, and the rate constants to form ROONO are calculated to be 3 x 10(-12) to 2 x 10(-11) cm(3) molecule(-1) s(-1) using the canonical variational transition state theory. The vRRKM/ME analysis reveals negligible stabilization of excited ROONO and provides an assessment of ROONO isomerization to RONO2.