Section: 9 | Spectroscopic Constants of Diatomic Molecules |

How to Cite this Reference

SPECTROSCOPIC CONSTANTS OF DIATOMIC MOLECULES

David R. Lide

This table lists the leading spectroscopic constants and equilibrium internuclear distance r_e in the ground electronic state for selected diatomic molecules. The constants are those describing the vibrational and rotational energy through the expressions:

E_vib/hc = ω_e(v + ½) – ω_ex_e(v + ½)² + •••

E_rot/hc = B_vJ(J + 1) – D_v[J(J + 1)]² + •••

where

B_v = B_e – α_e(v + ½) + •••

D_v = D_e + •••

Here v and J are the vibrational and rotational quantum numbers, respectively, h is Planck’s constant, and c is the speed of light. In this customary formulation the constants ω_e , B_e, etc., have dimensions of inverse length; in this table they are given in units of cm^–1.

Users should note that higher order terms in the above energy expressions are required for very precise calculations. The references contain constants for many of these higher terms, as well as more precise values of the lower constants. Also, if the ground electronic state is not ¹Σ, additional terms are needed to account for the interaction between electronic and pure rotational angular momentum. For some molecules in the table, the data have been analyzed in terms of the Dunham series expansion:

E/hc = Σ_lmY_lm(v + ½)^lJ ^m(J + 1)^m

In such cases it has been assumed that Y₁₀ = ω_e , Y₀₁ = B_e , etc., although in the highest ,approximations these identities are not precisely correct. Some of the values of r_e in the table have been corrected for breakdown of the Born-Oppenheimer approximation, which can affect the last decimal place. Because of differences in the method of data analysis and limitations in the model, care should be taken in comparing r_e values for different molecules to a precision beyond 0.001 Å. Column definitions are as follows.

Column heading	Definition
Mol. form.	Molecular formula of diatomic molecule; molecules are listed in alphabetical order by formula as most commonly written. In most cases this form places the more electropositive element first, but there are exceptions such as OH, NH, CH, etc.
Molecule	Isotopic specification of the diatomic molecule; superscripts indicate isotope for each element of the diatomic molecule
State	Spectroscopic state symbol
ω_e	Vibrational constant — first term, in cm^-1; entries in the ω_e column that are marked by * give the interval between v = 0 and v = 1 states instead of a value of ω_e
ω_ex_e	Vibrational constant — second term, in cm^-1
B_e	Rotational constant in equilibrium position, in cm^-1
α_e	Rotational constant — first term, in cm^-1
D_e	Centrifugal distortion constant, in cm^-1
r_e	Equilibrium internuclear distance, in Å
Ref.	Reference number

Refs. 1–5 are evaluated compilations covering many molecules and giving references to the original literature.

References

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Mobile-friendly table

Spectroscopic Constants of Diatomic Molecules

Mol. form.	Name	CAS Reg. No.	Molecule	State	ω_e/cm^-1	ω_ex_e/cm^-1	B_e/cm^-1	α_e/cm^-1	D_e/10^-6 cm^-1	r_e/Å	Ref.
Continued on next page...
AgBr	Silver(I) bromide	7785-23-1	¹⁰⁷Ag⁷⁹Br	¹Σ⁺	249.57	0.63	0.064833	0.0002361	0.0175	2.39311	1,2,3
AgCl	Silver(I) chloride	7783-90-6	¹⁰⁷Ag³⁵Cl	¹Σ⁺	343.49	1.17	0.12298388	0.00059541	0.06305	2.28079	1,2,3
AgD	Silver(I) hydride-d	13816-78-9	¹⁰⁷Ag²H	¹Σ⁺	1250.70	17.17	3.2572	0.0722	85.9	1.6180	1,2
AgF	Silver(I) fluoride	7775-41-9	¹⁰⁷Ag¹⁹F	¹Σ⁺	513.45	2.59	0.2657020	0.0019206	0.284	1.98318	1,2,3
AgH	Silver(I) hydride	13967-01-6	¹⁰⁷Ag¹H	¹Σ⁺	1759.9	34.06	6.449	0.201	344	1.618	1,2
AgI	Silver(I) iodide	7783-96-2	¹⁰⁷Ag¹²⁷I	¹Σ⁺	206.50	0.46	0.04486821	0.0001414	0.00847	2.54463	1,2,3
AgO	Silver(II) oxide	1301-96-8	¹⁰⁷Ag¹⁶O	²Π_1/2	490.2	3.1	0.3020	0.0025	0.45	2.003	1,2
AlBr	Aluminum monobromide	22359-97-3	²⁷Al⁷⁹Br	¹Σ⁺	378.0	1.28	0.15919713	0.00086045	0.11285	2.29481	1,2
AlCl	Aluminum monochloride	13595-81-8	²⁷Al³⁵Cl	¹Σ⁺	481.77	2.10	0.24393007	0.00161108	0.25017	2.13014	7
AlD	Aluminum monohydride-d	22737-86-6	²⁷Al²H	¹Σ⁺	1211.77	15.06	3.3183929	0.0698773	99.42	1.64637	17
AlF	Aluminum monofluoride	13595-82-9	²⁷Al¹⁹F	¹Σ⁺	802.32	4.85	0.55248021	0.00498426	1.0464	1.65437	4,5
AlH	Aluminum monohydride	13967-22-1	²⁷Al¹H	¹Σ⁺	1682.37	29.05	6.3937842	0.1870527	368.53	1.64736	17
AlI	Aluminum monoiodide	29977-41-1	²⁷Al¹²⁷I	¹Σ⁺	316.1	1.0	0.11769985	0.00055859		2.53710	1,2
AlO	Aluminum monoxide	14457-64-8	²⁷Al¹⁶O	²Σ⁺	979.49	7.01	0.6413856	0.0057796	1.08	1.61782	4
AlS	Aluminum monosulfide	12251-90-0	²⁷Al³²S	²Σ⁺	617.11	3.33	0.2800368	0.0017823	0.22	2.02828	4
Al₂	Dialuminum	32752-94-6	²⁷Al₂	³Π_u	285.8	0.9	0.17127	0.0008		2.701	1,2
AsD	Arsenic monohydride-d	17534-23-5	⁷⁵As²H	³Σ^-	1484^*		3.6688		90	1.5306	1,2
AsH	Arsenic monohydride	12628-08-9	⁷⁵As¹H	³Σ^-	2130^*		7.3067	0.2117	327	1.52315	1,2
AsN	Arsenic nitride	26754-98-3	⁷⁵As¹⁴N	¹Σ⁺	1068.54	5.41	0.54551	0.003366	0.53	1.6184	1,2

* Indicates a value for the interval between v = 0 and v = 1 states instead of a value of ω_e.

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