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Updated: Mar 8, 2026

Computation of Atmospheric Concentrations of Molecular Clusters from ab initio Thermochemistry
Published on: April 8, 2020
Conformational structures of jet-cooled acetaminophen-water clusters: a gas phase spectroscopic and computational
Ahreum Min1, Ahreum Ahn1, Cheol Joo Moon1
1Department of Chemistry (BK21+) and Research Institute of Natural Science, Gyeongsang National University, Jinju 52828, Republic of Korea. mychoi@gnu.ac.kr.
Abstract:
Jet-cooled acetaminophen (AAP)-water clusters, AAP-(H2O)1, were investigated by mass-selected resonant two-photon ionization (R2PI), ultraviolet-ultraviolet hole-burning (UV-UV HB), infrared-dip (IR-dip), and infrared-ultraviolet hole-burning (IR-UV HB) spectroscopy. Each syn- and anti-AAP rotamer has three distinctive binding sites (-OH, >CO, and >NH) for a water molecule, thus 6 different AAP-(H2O)1 conformers are expected to exist in the molecular beam. The origin bands of the AAP(OH)-(H2O)1 and AAP(CO)-(H2O)1 conformers (including their syn- and anti-conformers) in the R2PI spectrum are shifted to red and blue compared to those of the AAP monomer, respectively. These frequency shifts upon complexation between a water molecule and a specific binding site of AAP are also predicted by theoretical calculations. The spectral assignments of the origin bands in the R2PI spectra and the IR vibrational bands in the IR-dip spectra of the four lowest-energy conformers of AAP-(H2O)1, [syn- and anti-AAP(OH)-(H2O)1 and syn- and anti-AAP(CO)-(H2O)1], are aided by ab initio and time-dependent density functional theory (TDDFT) calculations. Further investigation of the IR-dip spectra has revealed a hydrogen-bonded NH stretching mode, supporting the presence of the syn-AAP(NH)-(H2O)1 conformer. Moreover, by employing IR-UV HB spectroscopy, we have reconfirmed the existence of the syn-AAP(NH)-(H2O)1 conformer, which happened to be buried underneath the broad background contributed by the AAP(OH)-(H2O)1 conformers. These observations have led us to conclude that all of the possible conformers of AAP-(H2O)1 have been found in this study.
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