68 th OSU International Symposium on Molecular Spectroscopy

68 th OSU International Symposium on Molecular Spectroscopy MH 09 The complete molecular geometry of salicyl aldehyde from rotational spectroscopy Orest Dorosh, Ewa Białkowska-Jaworska, Zbigniew Kisiel, Lech Pszczółkowski, Institute of Physics, Polish Academy of Sciences, Warszawa, Poland Marianna Kańska, Tadeusz M. Krygowski Department of Chemistry, University of Warsaw, Warszawa, Poland Heinrich Mäder Institut für Physikalische Chemie, Christian Albrechts Universität zu Kiel, Germany

Some background on salicyl aldehyde: Jones and Curl: J. Mol. Spectrosc. 42, 65 (1972) 1. 76(1) Å “Microwave spectrum of salicyl aldehyde: Structure of the Hydrogen Bond” Only ma , R-type transitions measured at 26. 5 -40 GHz + rigid rotor analysis

Overview of our salicyl aldehyde work: ð As already reported, RI 12 OSU 2006: The room temperature MMW spectrum and supersonic expansion FTMW spectra were used to determine precise values of spectroscopic constants for the parent species ð Calculated force field was scaled to reproduce the quartics and then used to calculate quartics for the isotopic species ð Multiple isotopic species were measured with supersonic exp. FTMW, either in natural abundance or in synthethic samples ð Electric dipole moment also measured ð Problem: considerable variation in structural parameters between rs, r 0, rm(1) geometries in the region of the central C(1)-C(2) bond ð Current solution: Another spectrometer (waveguide FTMW) brought in to measure excited vibrational states in order to calibrate ab initio Bv-B 0 calculations ð The preferred re. SE geometry evaluated

Substitution coordinates (Å) for salicyl aldehyde:

Structural analysis options: , a = a, b, c Ground state Equilibrium Measured Vibration-rotation contribution consisting of harmonic and anharmonic terms ð Ignore є 0: rs, r 0 ð Treat є 0 as a parameter of fit: rm(1). . . ð Precalculate є 0 from anharmonic ab initio force field: re. SE Program STRFIT from the PROSPE site was used for the analysis (allows r 0, rm(1), rm(1 L) , rm(2) , re. SE fits)

The band nature of the MMW spectrum of salicyl aldehyde: The bands are of type-II and consist of overlaps of a. R- and b. R- transitions for different J. Band appearance is critically dependent on the inertial defect. J”=104 Obs. g. s. v 37 v 38 v 39 Calc.

Lowest vibrational energy levels in salicyl aldehyde: ð Only the two lowest excited vibrational states unperturbed ð MMW transitions in the next three states carry various signatures of mutual perturbations ð While testing the newly relocated waveguide FTMW spectrometer it was found that the lower J and Ka transitions accessible to it are largely free from the effects of perturbation The 8 -18 GHz waveguide FTMW spectrometer with auto scanning: M. Kruger, H. Dreizler, Z. Naturforsch. 45 a, 724 (1990) M. Kruger, H. Harder, C. Gerke, H. Dreizler, Z. Naturforsch. 48 a, 737 (1993)

The 8 -18 GHz waveguide FTMW spectrometer : 12 m waveguide cell Salicyl aldehyde sample

Sample cell and LO line of the waveguide FTMW spectrometer: Detector station Wall passage

The region of the a. R-branch 53, 3 43, 2 transition: Synthetic spectrum made with VKIEL, PROSPE website * * * v 27 * v 38 g. s. Obs. * * v 37 v 39 2 v 39 Calc.

The region of the b. Q-branch 134, 9 133, 10 transition: * * Obs. * * v 37 v 38 2 v 39 v 27 Calc. g. s.

Calibration of anharmonic Bv-B 0 calculations: Results for the two lowest excited vibrational states for which the MMW rotational transitions are unperturbed Calculations made with CFOUR at the MP 2/DZP level (165 basis functions, 12 days on an i 7 computer) Inertial defect, -0. 090865(13) uÅ2 for the ground state

Calibration of anharmonic Bv-B 0 calculations: Results for the next three vibrational states for which the MMW rotational transitions are known to be mutually perturbed

Isotopologues used for structure determination: Number Type 1 parent 2 7 6 18 O 5 1 1 1 2 _____ = 26 13 C d 1 d 2 d 3 d 4 d 5 13 C, D All 15 singly substituted isotopologues: Heavy nuclei in natural abundance DO substitution with D 2 O, other D from three different reactions to substitute at C 7 (DCO), C 3+C 5, and C 4+C 6 Also additional isotopologues obtained as a byproduct or by deuterating other samples further with D 2 O

The complete re. SE geometry of salicyl aldehyde:

Comparison of salicyl aldehyde bond lengths: 6 -311++G(d, p)

Comparison of salicyl aldehyde angles: 6 -311++G(d, p)

CONCLUSIONS: ð Previous MMW and supersonic expansion cavity FTMW measurements were augmented with room-temperature waveguide FTMW data to determine perturbation free spectroscopic constants for the five lowest excited vibrational states ð The excited state rotational constants served to calibrate the ab initio anharmonic calculation of Bv-B 0 values (made with CFOUR) and the MP 2/DZP level proved to be cost effective for this molecule ð The complete re. SE geometry was determined and it seems to be in best agreement with electron diffraction and computed data, while rs and rm(1) seem to be susceptible to artefacts resulting from several small inertial coordinates ð Room-temperature FTMW rotational spectroscopy currently seems to be the main alternative/replacement technique to Stark spectroscopy for complementing MMW and supersonic-expansion FTMW measurements