Ab initio thermal rate coefficients for H + NH 3 ⇌ H 2 + NH 2

The reversible reaction NH 3 + H ⇌ H 2 + NH 2 , which plays an important role in NH 3 fuel combustion, is studied with a theoretical approach that combines the high‐accuracy extrapolated ab initio thermochemistry (HEAT) protocol with semiclassical transition state theory (SCTST). The calculated forward reaction is endothermic by 11.8 ± 1 kJ/mol, in nearly perfect agreement with the active thermochemical tables (ATcT) value of 11.5 ± 0.2 kJ/mol. Using this improved thermochemistry yields better rate constants, especially at low temperatures. Experimental rate constants available from 400 to 2000 K for the forward and reverse reaction pathways can be reproduced (within 20%) by the calculations from first principles.