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National Institute of Standards and Technology NIST Physical Measurement Laboratory
NIST Atomic Spectra Database
Ionization Energies Data

U (all spectra)
92 Data Rows Found 
Example of how to reference these results:
Kramida, A., Ralchenko, Yu., Reader, J., and NIST ASD Team (2024). NIST Atomic Spectra Database (ver. 5.12), [Online]. Available: https://physics.nist.gov/asd [2026, October 26]. National Institute of Standards and Technology, Gaithersburg, MD. DOI: https://doi.org/10.18434/T4W30F
BibTex Citation (new window)
 

 Ionization  Energy 
 (cm-1) 
  49 958.4         
  93 500           
  159 700           
  296 000           
  (371 000)          
  [500 000]          
  (718 000)          
  (815 000)          
  (936 000)          
  (1 040 000)          
  (1 274 000)          
  (1 395 000)          
  (1 694 000)          
  (1 831 000)          
  (2 605 000)          
  (2 807 000)          
  (3 025 000)          
  (3 242 000)          
  (3 476 000)          
  (3 694 000)          
  (4 009 000)          
  (4 234 000)          
  (4 493 000)          
  (4 718 000)          
  (5 893 000)          
  (6 176 000)          
  (6 460 000)          
  (6 740 000)          
  (7 480 000)          
  (7 790 000)          
  (8 650 000)          
  (8 970 000)          
  (9 780 000)          
  (10 390 000)          
  (11 010 000)          
  (11 623 000)          
  (12 240 000)          
  (12 850 000)          
  (13 470 000)          
  (14 080 000)          
  (14 790 000)          
  (15 420 000)          
  (16 040 000)          
  (16 700 000)          
  (17 300 000)          
  (17 900 000)          
  (20 793 000)          
  (21 341 000)          
  (21 922 000)          
  (22 535 000)          
  (23 124 000)          
  (23 697 000)          
  (24 785 000)          
  (25 382 000)          
  (26 036 000)          
  (26 624 000)          
  (29 052 000)          
  (29 641 000)          
  (30 270 000)          
  (30 867 000)          
  (33 988 000)          
  (34 674 000)          
  (36 400 000)          
  [37 082 800]          
  (59 629 000)          
  (60 927 000)          
  (62 331 000)          
  (63 823 000)          
  (65 234 000)          
  (66 605 000)          
  (69 743 000)          
  (71 195 000)          
  (72 792 000)          
  (74 251 000)          
  (78 365 000)          
  (79 623 000)          
  (81 018 000)          
  (82 301 000)          
  (92 044 000)          
  (93 593 000)          
  (96 674 000)          
  (98 117 000)          
  (203 720 000)          
  (207 147 000)          
  (210 946 000)          
  (214 431 000)          
  (250 532 000)          
  (255 202 000)          
  (261 114 000)          
  (264 844 000)          
  (1 045 051 800)          
  (1 063 169 000)          
Notes:
a Uncertainty of the listed value is unknown.

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