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Conformationally resolved structures of jet-cooled acetaminophen by UV–UV hole-burning spectroscopy
Lee, Seung Jun,Min, Ahreum,Kim, Yusic,Ahn, Ahreum,Chang, Jinyoung,Lee, Sang Hak,Choi, Myong Yong,Kim, Seong Keun Royal Society of Chemistry 2011 Physical chemistry chemical physics Vol.13 No.37
<P>The conformational structures of jet-cooled acetaminophen were investigated in the gas phase by resonant 2-photon ionization and UV–UV hole-burning spectroscopy. In contrast to the results from a previous study, two nearly isoenergetic conformers were distinctly found in a supersonic molecular beam expansion and positively identified as the <I>cis</I> and <I>trans</I> isomers of acetaminophen by UV–UV hole-burning spectroscopy. The 0–0 bands of the <I>cis</I> and <I>trans</I> isomers were found at 33518.7 and 33485.6 cm<SUP>−1</SUP>, respectively. The vibronic bands of the two isomers are close-lying and/or partially overlapping due to the small energy difference (33 cm<SUP>−1</SUP>) between the two 0–0 bands. As a consequence, the recorded resonant 2-photon ionization spectrum is highly congested in the low excitation energy region, which develops continuously into a featureless, broadened spectrum in the high energy region.</P> <P>Graphic Abstract</P><P>Two ground state conformational isomers of acetaminophen, paracetamol, in its <I>cis</I>- and <I>trans</I>- forms, have been clearly and positively identified. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c1cp21999e'> </P>
Infrared Spectroscopy of Imidazole Trimer in Helium Nanodroplets: Free NH Stretch Mode
Seulki Lee,Seung Jun Lee,Ahreum Ahn,Yusic Kim,민아름,최명룡,Roger E. Miller 대한화학회 2011 Bulletin of the Korean Chemical Society Vol.32 No.3
We report the first vibrational band assignment of imidazole trimer (IMT) solvated in helium nanodroplets. Several congested vibrational bands of imidazole (IM) clusters were obtained in the frequency region of 3513-3515 cm^(−1) and vibrationally resolved due to the extremely low temperature (0.37 K) and very weak solutesolvent interaction environments of helium droplets. The unambiguous free NH band assignment was achieved with an aid of pick-up oven temperature dependence and vibrational transition moment angle (VTMA)experiments as well as density functional theory (DFT) calculations. The band at 3514.3 cm^(−1) is attributed to the free NH stretching mode of linear IMT clusters, easily formed by the dipole-dipole interactions of IM in ultracold helium nanodroplets.