Calculated and experimentally measured bond lengths (in Å) for diatomic halogens^a.

Halogen	F–F	Cl–Cl	Cl–F	Br–Br	Br–F	Br–Cl	I–I	I–F	I–Cl	I–Br
B3LYP/DGDZVP (this paper)	1.411	2.057	1.671	2.341	1.811	2.200	2.744	1.983	2.399	2.538
Experimental X-ray or neutron diffraction in crystal or liquid	α: 1404 (ref. 67)	1.991;68 1.985;69 1.994 (ref. 64)	1.628 (ref. 69)	2.301 (ref. 64)	1.822 (ref. 70) in complex with CH3Cl	2.178 (ref. 70)	2.715;71 2.710 (ref. 65)		α: 2.37, 2.44;72β: 2.35, 2.44 (ref. 73)	2.52 (ref. 74)
Experimental spectroscopy in gas	1.4119 (ref. 75)	1.9879 (ref. 75)	1.628 (ref. 75)	2.281 (ref. 75)	1.759 (ref. 76)	2.138 (ref. 77)	2.666 (ref. 75)	1.9097 (ref. 75)	2.321 (ref. 77)	2.469 (ref. 75)
Computational	1.415;67 1.4181 (ref. 79)	2.0195;79 2.028 (ref. 81)	1.6464 (ref. 79)	2.279 (ref. 66)	1.736 (ref. 70)	2.1435 (ref. 78)	2.798;65 2.654 (ref. 66)	1.9110 (ref. 78)	2.313;66 2.513 (ref. 80)	2.462;66 2.677 (ref. 80)

^aCcomputations were made in B3LYP-D/DZV,⁶⁵ PBE0/def2-TZVPPD,⁶⁶ CCSD(T) aug-cc-pVTZ/,⁶⁷ MP2/aug-cc-pVTZ,⁷⁰ CCSD(T)/aug-cc-pV(5+d)Z and CCSD(T)/aug-cc-pRV5Z,⁷⁸ CCSD(T)/aug-cc-pVTZ,⁷⁹ B3LYP/LANL2DZ,⁸⁰ and MP2/6-311++G(2D)⁸¹ (for dimer). For a large set of precise computations for dihalogens, see ref. 78.