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We report the first observation of the symmetric CH stretch fundamental level (\u03bd1\u2032), and of the out-of-plane bend with the antisymmetric CH stretch combination level (\u03bd4\u2032+\u03bd5\u2032) including rotational analysis, using infrared\u2013ultraviolet double-resonance laser-induced fluorescence spectroscopy. The experimental results agree very well with full-dimensional ab\u00a0initio quasi-variational discrete variable representation calculations on a frozen core equation of motion coupled cluster (EOM-CCSDT\/ANO1) surface. We compare our findings with various models, including effective potentials, a semiclassical approach, and a quasidiabatic vibronic coupling treatment, to derive insights into the dynamics and coupling between different degrees of freedom in the vicinity of the tunneling barrier.<\/jats:p>","DOI":"10.1063\/5.0297053","type":"journal-article","created":{"date-parts":[[2025,10,21]],"date-time":"2025-10-21T10:34:35Z","timestamp":1761042875000},"update-policy":"https:\/\/doi.org\/10.1063\/aip-crossmark-policy-page","source":"Crossref","is-referenced-by-count":1,"title":["Mode-specific low barrier tunneling dynamics in the A\u0303 state of formaldehyde: The\n                    <i>\u03bd<\/i>\n                    1 fundamental and\n                    <i>\u03bd<\/i>\n                    4 +\n                    <i>\u03bd<\/i>\n                    5 combination levels"],"prefix":"10.1063","volume":"163","author":[{"ORCID":"https:\/\/orcid.org\/0009-0008-8063-0841","authenticated-orcid":false,"given":"Maayan","family":"Cohen","sequence":"first","affiliation":[{"name":"Department of Chemistry, Ben-Gurion University of the Negev 1 , 8410501 Beer Sheva,","place":["Israel"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4591-2279","authenticated-orcid":false,"given":"Nadav","family":"Genossar-Dan","sequence":"additional","affiliation":[{"name":"Department of Chemistry, Ben-Gurion University of the Negev 1 , 8410501 Beer Sheva,","place":["Israel"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0304-9814","authenticated-orcid":false,"given":"P. 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