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

Np (all spectra)
93 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) 
  50 535.54         
  [93 000]           
  [159 000]           
  [273 000]           
  (387 000)           
  (524 000)           
  (743 200)           
  (861 000)           
  (978 000)           
  (1 096 000)           
  (1 220 000)           
  (1 444 000)           
  (1 581 000)           
  (1 879 000)           
  (2 033 000)           
  (2 863 000)           
  (3 081 000)           
  (3 291 000)           
  (3 533 000)           
  (3 759 000)           
  (3 992 000)           
  (4 315 000)           
  (4 557 000)           
  (4 807 000)           
  (5 049 000)           
  (6 243 000)           
  (6 533 000)           
  (6 820 000)           
  (7 110 000)           
  (7 890 000)           
  (8 220 000)           
  (9 090 000)           
  (9 420 000)           
  (10 300 000)           
  (10 930 000)           
  (11 550 000)           
  (12 179 000)           
  (12 810 000)           
  (13 440 000)           
  (14 070 000)           
  (14 700 000)           
  (15 420 000)           
  (16 060 000)           
  (16 700 000)           
  (17 300 000)           
  (18 000 000)           
  (18 600 000)           
  (21 575 000)           
  (22 140 000)           
  (22 721 000)           
  (23 342 000)           
  (23 947 000)           
  (24 527 000)           
  (25 656 000)           
  (26 253 000)           
  (26 923 000)           
  (27 528 000)           
  (29 988 000)           
  (30 585 000)           
  (31 230 000)           
  (31 835 000)           
  (35 109 000)           
  (35 819 000)           
  (37 569 000)           
  (38 263 000)           
  (61 355 000)           
  (62 685 000)           
  (64 097 000)           
  (65 605 000)           
  (67 049 000)           
  (68 428 000)           
  (71 678 000)           
  (73 146 000)           
  (74 760 000)           
  (76 252 000)           
  (80 413 000)           
  (81 696 000)           
  (83 107 000)           
  (84 406 000)           
  (94 649 000)           
  (96 214 000)           
  (99 351 000)           
  (100 819 000)           
  (208 631 000)           
  (212 092 000)           
  (215 947 000)           
  (219 480 000)           
  (257 404 000)           
  (262 162 000)           
  (268 195 000)           
  (271 988 000)           
  (1 072 000 000)           
  (1 090 480 000)           
Notes:
a Uncertainty of the listed value is unknown.

If you did not find the data you need, please inform the ASD Team.

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