{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,11]],"date-time":"2026-08-11T12:41:17Z","timestamp":1786452077418,"version":"build-2736575974"},"reference-count":53,"publisher":"AIP Publishing","issue":"6","content-domain":{"domain":["pubs.aip.org"],"crossmark-restriction":true},"short-container-title":[],"published-print":{"date-parts":[[2026,8,14]]},"abstract":"<jats:p>The longer time scale of water reorientation is intimately coupled to H-bond exchange, as elucidated by the jump reorientation mechanism proposed by Laage and Hynes. Here, we revisit this mechanism to probe the short-to-intermediate time scales of the reorientation process. Analysis of the reorientation time correlation function (TCF) of bulk water reveals an intermediate time scale of \u223c1.15 ps contributing nearly 20% of the total decay. To elucidate its molecular origin, we further analyze the TCF of the donor O*\u2013H* vector over the interval preceding an H-bond exchange event, removing contributions from the transition-state region, which reveals the same \u223c1.15 ps component along with a slower \u223c6 ps frame-tumbling motion. A wobbling-in-a-cone analysis reveals that this intermediate relaxation time scale originates from an effective coupling between the second wobbling motion and the final orientational randomization process. This regime involves a broader angular exploration of the donor O*\u2013H* bond (\u223c33\u00b0\u201335\u00b0) with an associated relaxation time scale of \u223c1.38 ps before randomization. Further trajectory analysis reveals acceptor-free dangling states of the donor between successive successful exchange events, where short-lived states (\u226420 fs) arise mainly from angular fluctuations, while longer dangling stretches (\u226550 fs) involve increased donor\u2013acceptor distance and populate a near transition-state-like region (\u223c3.5 \u00c5, \u223c30\u00b0), although distinct from an exact transition-state configuration. The average waiting time of such long-lived dangling events is \u223c1.07\u00a0ps. Interestingly, the time scale of the second wobbling motion closely matches the average waiting time of long-lived dangling stretches, indicating unsuccessful hydrogen-bond switching attempts drive intermediate reorientation dynamics. We believe similar analysis will be useful for breaking down time scales observed in various confined systems.<\/jats:p>","DOI":"10.1063\/5.0344940","type":"journal-article","created":{"date-parts":[[2026,8,11]],"date-time":"2026-08-11T12:20:44Z","timestamp":1786450844000},"update-policy":"https:\/\/doi.org\/10.1063\/aip-crossmark-policy-page","source":"Crossref","is-referenced-by-count":0,"title":["Revisiting orientational relaxation in bulk water: Observation and mechanistic understanding of an intermediate time scale (around 1\u00a0ps)"],"prefix":"10.1063","volume":"165","author":[{"given":"Subhabrata","family":"Hazra","sequence":"first","affiliation":[{"name":"School of Chemical Science, Indian Association for the Cultivation of Science , Jadavpur, Kolkata 700032,","place":["India"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7684-1963","authenticated-orcid":false,"given":"Biman","family":"Jana","sequence":"additional","affiliation":[{"name":"School of Chemical Science, Indian Association for the Cultivation of Science , Jadavpur, Kolkata 700032,","place":["India"]}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"317","published-online":{"date-parts":[[2026,8,11]]},"reference":[{"issue":"1","key":"2026081107475607900_c1","doi-asserted-by":"publisher","first-page":"74","DOI":"10.1021\/cr068037a","article-title":"Water as an active constituent in cell biology","volume":"108","year":"2008","journal-title":"Chem. 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