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

68th OSU International Symposium on Molecular Spectroscopy MH0968th OSU International Symposium on Molecular Spectroscopy MH09

1.76(1) Å

Jones and Curl: J.Mol.Spectrosc. 42, 65 (1972)

“Microwave spectrum of salicyl aldehyde: Structure of the Hydrogen Bond”

Only ma , R-type transitions measured at 26.5-40 GHz + rigid rotor analysis

Some background on salicyl aldehyde:

Overview of our salicyl aldehyde work:

As already reported, RI12 OSU2006: The room temperature MMW spectrum and supersonic expansion FTMW spectra were used to determine precise values of spectroscopic constants for the parent species

Calculated force field was scaled to reproduce the quartics and then used to calculate quartics for the isotopic species

Multiple isotopic species were measured with supersonic exp. FTMW, either in natural abundance or in synthethic samples

Electric dipole moment also measured

Problem: considerable variation in structural parameters between rs, r0, rm

(1) geometries in the region of the central C(1)-C(2) bond

Current solution: Another spectrometer (waveguide FTMW) brought in to measure excited vibrational states in order to calibrate ab initio Bv-B0 calculations

The preferred reSE geometry evaluated

Substitution coordinates (Å) for salicyl aldehyde:

Ground state

Measured

Equilibrium Vibration-rotation contribution consisting of harmonic andanharmonic terms

, a = a, b, c

Structural analysis options:

Ignore є0: rs, r0

Treat є0 as a parameter of fit: rm(1)...

Precalculate є0 from anharmonic ab initio force field: reSE

Program STRFIT from the PROSPE site was used for the analysis (allows r0, rm

(1), rm(1L) , rm

(2) , reSE fits)

The band nature of the MMW spectrum of salicyl aldehyde:

v39v37

v38g.s.

J”=104

The bands are of type-II and consist of overlaps of aR- and bR- transitions for different J. Band appearance is critically dependent on the inertial defect.

Obs.

Calc.

Lowest vibrational energy levels in salicyl aldehyde:

The 8-18GHz waveguide FTMW spectrometer with auto scanning:

M.Kruger, H.Dreizler, Z.Naturforsch. 45a, 724 (1990)M.Kruger, H.Harder, C.Gerke, H.Dreizler, Z.Naturforsch. 48a, 737 (1993)

Only the two lowest excited vibrational states unperturbed

MMW transitions in the next three states carry various signatures of mutual perturbations

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 8-18GHz waveguide FTMW spectrometer :

12m waveguide cell

Salicyl aldehyde sample

Sample cell and LO line of the waveguide FTMW spectrometer:

Detector station

Wall passage

The region of the aR-branch 53,343,2 transition:

Obs.

Calc.v39

v27

v37v38 2v39

g.s.

**

*

*

* *

Synthetic spectrum made with VKIEL, PROSPE website

The region of the bQ-branch 134,9133,10 transition:

Obs.

Calc.v39

v27

v37

v38 2v39

g.s.

*

*

*

* *

*

Calibration of anharmonic Bv-B0 calculations:

Results for the two lowest excited vibrational states for which the MMW rotational transitions are unperturbed

Calculations made with CFOUR at the MP2/DZP level (165 basis functions, 12 days on an i7 computer)

Inertial defect, -0.090865(13) uÅ2 for the ground state

Calibration of anharmonic Bv-B0 calculations:

Results for the next three vibrational states for which the MMW rotational transitions are known to be mutually perturbed

Number Type

1 parent

2 18O7 13C6 d1

5 d2

1 d3

1 d4

1 d5

2 13C,D _____ = 26

Isotopologues used for structure determination:

Also additional isotopologues obtained as a by-product or by deuterating other samples further with D2O

All 15 singly substituted isotopologues:

Heavy nuclei in natural abundance

DO substitution with D2O, other D from three different reactions to substitute at C7 (DCO), C3+C5, and C4+C6

The complete reSE 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)

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

The excited state rotational constants served to calibrate the ab initio anharmonic calculation of Bv-B0 values (made with CFOUR) and the MP2/DZP level proved to be cost effective for this molecule

The complete reSE 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

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

CONCLUSIONS: