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Here, we combine high-level ab\u00a0initio calculations to unambiguously identify radicals via their structures, energies, and internal dynamics with a very sensitive high-resolution millimeter wave spectroscopy (150\u2013500\u00a0GHz) setup to resolve and characterize the two isomeric forms of dehydrogenated methyl formate: the formyloxymethyl radical (CH2OCHO) and the methoxy carbonyl radical (CH3OCO). Our results demonstrate that millimeter wave spectroscopy enables the direct, isomer-specific detection of medium-sized dehydrogenated VOCs\u2014a critical advancement for oxidation experiments and environmental monitoring. This integrated approach paves the way for real-time tracking of radical intermediates under diverse atmospheric conditions, with broad implications for understanding VOC degradation pathways.<\/jats:p>","DOI":"10.1063\/5.0345772","type":"journal-article","created":{"date-parts":[[2026,9,22]],"date-time":"2026-09-22T12:13:02Z","timestamp":1790079182000},"update-policy":"https:\/\/doi.org\/10.1063\/aip-crossmark-policy-page","source":"Crossref","is-referenced-by-count":0,"title":["Direct spectroscopic identification of elusive dehydrogenated radicals: CH2OCHO and CH3OCO radicals from methyl formate oxidation"],"prefix":"10.1063","volume":"165","author":[{"ORCID":"https:\/\/orcid.org\/0009-0009-1385-0745","authenticated-orcid":false,"given":"R.","family":"Chahbazian","sequence":"first","affiliation":[{"name":"Universit\u00e9 Paris-Saclay, CNRS, Institut des Sciences Mol\u00e9culaire d\u2019Orsay 1 , 91400 Orsay,","place":["France"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-1878-7377","authenticated-orcid":false,"given":"M. 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