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Such TSs are commonly referred to as ambimodal TSs. In contrast, conventional intrinsic reaction coordinate (IRC) calculations typically connect the TS to only one of the possible products and therefore fail to identify alternative non\u2010IRC products. To assess the ambimodal character of TSs in PTSB reactions, we analyzed relaxed pathways connecting a TS directly to a non\u2010IRC product using the double\u2010ended string method. Application of this approach to a total of 33 reaction systems, including pericyclic reactions (among them two trifurcation systems) and non\u2010pericyclic reactions, enabled unambiguous classification of TS\u2010product connections as either a static downhill connection or a static small\u2010barrier connection, depending on whether an energy maximum exists below the TS. The proposed method provides a practical and robust tool for the static topological analysis of PTSB reactions and serves as an effective complement to on\u2010the\u2010fly dynamical trajectory simulations.<\/jats:p>","DOI":"10.1002\/jcc.70517","type":"journal-article","created":{"date-parts":[[2026,9,29]],"date-time":"2026-09-29T05:26:48Z","timestamp":1790659608000},"update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Application of the String Method to Determine the Ambimodal Nature of Transition States in Bifurcation Reactions"],"prefix":"10.1002","volume":"47","author":[{"ORCID":"https:\/\/orcid.org\/0009-0007-2586-8059","authenticated-orcid":false,"given":"Keita","family":"Yamaki","sequence":"first","affiliation":[{"name":"Department of Chemistry Saitama University  Saitama 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