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The major objective of this work is to probe such coupling of the praseodymium (Pr) 4f and 6s electrons in Pr2O2 and Pr2O2+. The approach combines mass-analyzed threshold ionization spectroscopy and spin\u2013orbit multiconfiguration second-order quasi-degenerate perturbation theory. The energies of six ionization transitions are precisely measured; the adiabatic ionization energy of the neutral cluster is 38\u2009045 (5) cm\u22121. Most of the electronic states involved in these transitions are identified as spin\u2013orbit coupled states consisting of two or more electron spins. The electron configurations of these states are 4f46s2 for the neutral cluster and 4f46s for the singly charged cation, both in planar rhombus-type structures. The spin\u2013orbit splitting due to the coupling of the electrons on the separate Pr\u00a0atoms is on the order of hundreds of wavenumbers.<\/jats:p>","DOI":"10.1063\/5.0185579","type":"journal-article","created":{"date-parts":[[2023,12,22]],"date-time":"2023-12-22T10:59:12Z","timestamp":1703242752000},"update-policy":"https:\/\/doi.org\/10.1063\/aip-crossmark-policy-page","source":"Crossref","is-referenced-by-count":7,"title":["Spin\u2013orbit coupling of electrons on separate lanthanide atoms of Pr2O2 and its singly charged cation"],"prefix":"10.1063","volume":"159","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-7301-9752","authenticated-orcid":false,"given":"Taiji","family":"Nakamura","sequence":"first","affiliation":[{"name":"Department of Chemistry and Ames Laboratory 2 , Iowa State University, Ames, Iowa 50011-3111, USA"},{"name":"Institute for Materials Chemistry and Engineering 3 , Kyushu University, Nishi-ku, Fukuoka 819-0395, Japan"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1866-8725","authenticated-orcid":false,"given":"Beni B.","family":"Dangi","sequence":"additional","affiliation":[{"name":"Department of Chemistry, University of Kentucky 1 , Lexington, Kentucky 40506-0055, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Lu","family":"Wu","sequence":"additional","affiliation":[{"name":"Department of Chemistry, University of Kentucky 1 , Lexington, Kentucky 40506-0055, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Yuchen","family":"Zhang","sequence":"additional","affiliation":[{"name":"Department of Chemistry, University of Kentucky 1 , Lexington, Kentucky 40506-0055, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8624-5217","authenticated-orcid":false,"given":"George","family":"Schoendorff","sequence":"additional","affiliation":[{"name":"Department of Chemistry and Ames Laboratory 2 , Iowa State University, Ames, Iowa 50011-3111, USA"},{"name":"Propellants Branch, Rocket Propulsion Division, Aerospace Systems Directorate, Air Force Research Laboratory, AFRL\/RQRP, Edwards Air Force Base 4 , California 93524, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2371-1318","authenticated-orcid":false,"given":"Mark S.","family":"Gordon","sequence":"additional","affiliation":[{"name":"Department of Chemistry and Ames Laboratory 2 , Iowa State University, Ames, Iowa 50011-3111, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-9842-4343","authenticated-orcid":false,"given":"Dong-Sheng","family":"Yang","sequence":"additional","affiliation":[{"name":"Department of Chemistry, University of Kentucky 1 , Lexington, Kentucky 40506-0055, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"317","published-online":{"date-parts":[[2023,12,22]]},"reference":[{"key":"2023122210583421100_c1","doi-asserted-by":"publisher","first-page":"100411","DOI":"10.1016\/j.pquantelec.2022.100411","article-title":"Visible solid-state lasers based on Pr3+ and Tb3+","volume":"84","year":"2022","journal-title":"Prog. 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