Table 3.

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 crystal structure.

	State	ε	⟨R⟩
H	2	7.36	1.29
	1	3.76	1.34
	0	2.08	1.23
		RT	1.23
	2	4.77	1.28
D	1	2.63	1.39
	0	1.67	1.17
		RT	1.20

The bond length at the energy minimum is 1.06 Å. Thermally averaged bond lengths (R_T in Å) at room temperature are also shown.