Why does deuterium burn at lower temperature than H

[beee]

In general, nuclear fusion happens at a higher temperature for heavier elements. In my astrophysics class we derived an equation for probability of nuclear reactions, and without quoting it exactly, it boils down to have this probability proportional to exp(-m_rZ₁Z₂), where m_r is the reduced mass of colliding particles, Z_n are the atomic numbers.

So how come then, that deuterium burning occurs at roughly 10⁶K while regular hydrogen burns at 10⁷K?

 

[AdrianTheRock]

Fusing two ¹H to form deuterium also involves a weak force reaction, as one of the protons has to transform itself into a neutron (giving off a positron and an electron neutrino). Fusion of deuterium only involves the nuclear force.

 

[beee]

Makes perfect sense, thank you. As I see now, creating ²H is one of the steps in p-p chain of ¹H fusion, and rate limiting one at that. If you already have ²H, the fusion can take place at much lower temperatures.