Editing Rydberg constant (section)

{{Use American English|date = March 2019}}
{{Short description|Physical constants of energy and wavenumber}}
In [[spectroscopy]], the '''Rydberg constant''', symbol <math>R_\infty</math> for 
heavy atoms or <math>R_\text{H}</math> for hydrogen, named after the Swedish [[physicist]] [[Johannes Rydberg]], is a [[physical constant]] relating to the electromagnetic [[spectrum|spectra]] of an atom. The constant first arose as an empirical fitting parameter in the [[Rydberg formula]] for the [[hydrogen spectral series]], but [[Niels Bohr]] later showed that its value could be calculated from more fundamental constants according to his [[Bohr model|model of the atom]]. 

Before the [[2019 revision of the SI]], <math>R_\infty</math> and the electron spin [[g-factor (physics)|''g''-factor]] were the most accurately measured [[physical constant]]s.<ref name="pohl">{{cite journal |title=The size of the proton |journal=Nature |volume=466 |issue=7303 |pages=213–216|year=2010 |pmid=20613837|doi=10.1038/nature09250|bibcode = 2010Natur.466..213P |last2=Antognini |last3=Nez |last4=Amaro |last5=Biraben |last6=Cardoso |last7=Covita |last8=Dax |last10=Fernandes |first10=Luis M. P. |last11=Giesen |last12=Graf |last13=Hänsch |last14=Indelicato |last15=Julien |last16=Kao |last17=Knowles |last18=Le Bigot |last19=Liu |first19=Yi-Wei |last20=Lopes |first20=José A. M. |last21=Ludhova |last22=Monteiro |last23=Mulhauser |last24=Nebel |last25=Rabinowitz |last26=Dos Santos |last27=Schaller |last28=Schuhmann |last29=Schwob |first29=Catherine |last30=Taqqu |first30=David  |last1=Pohl |first1=Randolf |first2=Aldo |first3=François |first4=Fernando D. |first5=François |first6=João M. R. |first7=Daniel S. |first8=Andreas |last9=Dhawan |first9=Satish |first11=Adolf |first12=Thomas |first13=Theodor W. |first14=Paul |first15=Lucile |first16=Cheng-Yang |first17=Paul |first18=Eric-Olivier |first21=Livia |first22=Cristina M. B. |first23=Françoise |first24=Tobias |first25=Paul |first26=Joaquim M. F. |first27=Lukas A. |first28=Karsten |s2cid=4424731 }}</ref>

The constant is expressed for either hydrogen as <math>R_\text{H}</math>, or at the limit of infinite nuclear mass as <math>R_\infty</math>. In either case, the constant is used to express the limiting value of the highest [[wavenumber]] (inverse wavelength) of any photon that can be emitted from a hydrogen atom, or, alternatively, the wavenumber of the lowest-energy photon capable of ionizing a hydrogen atom from its [[ground state]]. The [[hydrogen spectral series]] can be expressed simply in terms of the Rydberg constant for hydrogen <math>R_\text{H}</math> and the [[Rydberg formula]].

In [[atomic physics]], '''Rydberg unit of energy''', symbol Ry, corresponds to the energy of the photon whose wavenumber is the Rydberg constant, i.e. the ionization energy of the hydrogen atom in a simplified Bohr model.{{cn|date=April 2019}}