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Title: Experimental and theoretical study on the excited-state dynamics of ortho-, meta-, and para-methoxy methylcinnamate

The S{sub 1} state dynamics of methoxy methylcinnamate (MMC) has been investigated under supersonic jet-cooled conditions. The vibrationally resolved S{sub 1}-S{sub 0} absorption spectrum was recorded by laser induced fluorescence and mass-resolved resonant two-photon ionization spectroscopy and separated into conformers by UV-UV hole-burning (UV-UV HB) spectroscopy. The S{sub 1} lifetime measurements revealed different dynamics of para-methoxy methylcinnamate from ortho-methoxy methylcinnamate and meta-methoxy methylcinnamate (hereafter, abbreviated as p-, o-, and m-MMCs, respectively). The lifetimes of o-MMC and m-MMC are on the nanosecond time scale and exhibit little tendency of excess energy dependence. On the other hand, p-MMC decays much faster and its lifetime is conformer and excess energy dependent. In addition, the p-MMC-H{sub 2}O complex was studied to explore the effect of hydration on the S{sub 1} state dynamics of p-MMC, and it was found that the hydration significantly accelerates the nonradiative decay. Quantum chemical calculation was employed to search the major decay route from S{sub 1}(ππ{sup ∗}) for three MMCs and p-MMC-H{sub 2}O in terms of (i) trans → cis isomerization and (ii) internal conversion to the {sup 1}nπ{sup ∗} state. In o-MMC and m-MMC, the large energy barrier is created for the nonradiative decay along (i) the double-bond twistingmore » coordinate (∼1000 cm{sup −1}) in S{sub 1} as well as (ii) the linear interpolating internal coordinate (∼1000 cm{sup −1}) from S{sub 1} to {sup 1}nπ{sup ∗} states. The calculation on p-MMC decay dynamics suggests that both (i) and (ii) are available due to small energy barrier, i.e., 160 cm{sup −1} by the double-bond twisting and 390 cm{sup −1} by the potential energy crossing. The hydration of p-MMC raises the energy barrier of the IC route to the S{sub 1}/{sup 1}nπ{sup ∗} conical intersection, convincing that the direct isomerization is more likely to occur.« less
Authors:
; ; ; ; ;  [1] ;  [2] ;  [3]
  1. Department of Chemistry, Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526 (Japan)
  2. Institute for Molecular Science and Research Center for Computational Science, 38 Myodaiji, Okazaki 444-8585 (Japan)
  3. (Japan)
Publication Date:
OSTI Identifier:
22415427
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 141; Journal Issue: 24; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
74 ATOMIC AND MOLECULAR PHYSICS; ABSORPTION SPECTRA; ABSORPTION SPECTROSCOPY; COMPLEXES; ENERGY DEPENDENCE; EXCITED STATES; FLUORESCENCE; HOLES; HYDRATION; INTERNAL CONVERSION; ISOMERIZATION; LASER RADIATION; LIFETIME; PHOTOIONIZATION; POTENTIAL ENERGY; S STATES; WATER