This table lists the leading spectroscopic constants and equilibrium internuclear distance re in the ground electronic state for selected diatomic molecules. The constants are those describing the vibrational and rotational energy through the expressions:
Evib/hc = ωe(v + ½) – ωexe(v + ½)2 + •••
Erot/hc = BvJ(J + 1) – Dv[J(J + 1)]2 + •••
where
Bv = Be – αe(v + ½) + •••
Dv = De + •••
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 ωe , Be , 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 = ΣlmYlm(v + ½)lJ m(J + 1)m
In such cases it has been assumed that Y10 = ωe , Y01 = Be , etc., although in the highest ,approximations these identities are not precisely correct. Some of the values of re 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 re values for different molecules to a precision beyond 0.001 Å. Column definitions for the table 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 |
ωe | Vibrational constant — first term, in cm-1; entries in the ωe column that are marked by * give the interval between v = 0 and v = 1 states instead of a value of ωe |
ωexe | Vibrational constant — second term, in cm-1 |
Be | Rotational constant in equilibrium position, in cm-1 |
αe | Rotational constant — first term, in cm-1 |
De | Centrifugal distortion constant, in cm-1 |
re | Equilibrium internuclear distance, in Å |
Ref. | Reference number |
Refs. 1–5 are evaluated compilations covering many molecules and giving references to the original literature.
Mol. form. | Name | CAS Reg. No. | Molecule | State | ωe/cm-1 | ωexe/cm-1 | Be/cm-1 | αe/cm-1 | De/10-6 cm-1 | re/Å | Ref. |
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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 | 2Π1/2 | 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 | 3Πu | 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 |
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