The Complete Molecular Geometry of Salicyl Aldehyde from Rotational Spectroscopy

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THE COMPLETE MOLECULAR GEOMETRY OF SALICYL ALDEHYDE FROM ROTATIONAL SPECTROSCOPY O. DOROSH, E. BIALKOWSKA-JAWORSKA, Z. KISIEL, L. PSZCZOLKOWSKI, Institute of Physics, Pol- ish Academy of Sciences, Al. Lotnikow´ 32/46, 02-668 Warszawa, Poland; M. KANSKA, T. M. KRYGOWSKI, Department of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warszawa, Poland; H. MAEDER, Insti- tut fur¨ Physikalische Chemie, Christian-Albrechts-Universitat¨ zu Kiel, Olshausenstrasse 40, D-24098 Kiel, Germany. Salicyl aldehyde is a well known planar molecule containing an internal hydrogen bond. In preparing the publication of our previous report of the study of its rotational spectruma we have taken the opportunity to update the structure determination of this molecule to SE the complete re geometry. The molecule contains 15 atoms and we have used supersonic expansion FTMW spectroscopy to obtain rotational constants for a total 26 different isotopic species, including all singly substitued species relative to the parent molecule. The 13 18 SE C and O substitutions were measured in natural abundance, while deuterium substitutions were carried out synthetically. The re determination requires the calculation of vibration-rotation changes in rotational constants from an ab initio anharmonic force field, which necessitates some compromises in the level of calculation for a molecule of the size of salicyl aldehyde. For this reason we studied the five lowest vibrationally excited states, by using the combination of room-temperature mm-wave spectroscopy and waveguide Fourier transform cm-wave spectroscopy. The experimental excited state rotational constants were then used to calibrate the anharmonic force SE field calculation. The resulting re geometry is compared with other types of geometry determination possible from this data, with emphasis on the effect of the near zero principal coordinate of the important C2 atom. aZ.Kisiel et al., 61st OSU Symposium on Molecular Spectroscopy, The Ohio State University, Ohio 2006, RI-12..

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