Table 2.

Vibrational energy levels (ε in kcal/mol) for the first three states and the averaged OH bond lengths (⟨R⟩ in Å) for a proton (H) and a deuteron (D) in hydrogen bond between Glu46 and pCA of PYP at the equilibrium structure.

	State	ε	⟨R⟩
H	2	10.14	1.21
	1	5.46	1.23
	0	2.02	1.17
		RT	1.17
D	2	6.52	1.22
	1	3.73	1.24
	0	1.47	1.15
		RT	1.15

The bond length at the energy minimum is 1.08 Å [17]. Thermally averaged bond lengths (R_T in Å) at room temperature are also shown.