1. F H F O
Semiexperimental structure of the non rigid BF2OH molecule (difluoroboric acid) by combining high resolution infrared spectroscopy and ab initio calculations.
Natalja Vogt, Jean Demaison, Section of Chemical Information Systems, Universität Ulm, Ulm, Germany;
Agnès Perrin, LISA, CNRS, Universités Paris Est Créteil et Paris Diderot, Créteil, France;
Hans Bürger, Anorganische Chemie, Bergische Universität Wuppertal, Wuppertal, Germany.

2. Introduction
Matrix infrared (IR) spectra of eight isotopologs, (Jacox et al. (J.C.P )
Several MW investigations (Takeo et al (1972), Vormann & Dreizler (1989),
MW & ab initio: Breidung et al (2004); Coudert et al. (2008)
Ab initio: Melendez et al. (2011).
FTIR in gas phase : Collet et al. (2002), Perrin et al. (2004, 2007,2012)

3. Introduction: ab initio: Breidung et al (2004)
The equilibrium geometry and anharmonic force fields have been calculated at the CCSD(T) level of theory.
The ab initio centrifugal distortion constants and rotation–vibration interaction constants were compared to the experimental values.
Some discrepancies are found and discussed. Particularly, it is explained why the semi-experimental structure is not reliable.
However…..
Informations on the n1, n2 and n3 infrared bands in gas phase at high resolution were missing.
Some of the vibration- rotation resonances were not accounted for during the energy level calculations of the 41, 61, 71, 81 and 91 vibrational states
Breidung, Demaison, D’Eu, Margulès, Collet, Mkadmi, A. Perrin, Thiel, J. Mol. Spectrosc. 228 (2004) p7

4. Infrared analyses: already published

5. Infrared analyses: large amplitude motionsOH
Torsion

6. Infrared analyses: large amplitude motionsOH
bending OH
Torsion

7. Infrared analyses:
numerous vibration- rotation resonances

8. New analysis

9. Accounting for additional resonances predicted by ab initio calculations

10. Outlook
The first high resolution investigation of the n1, n2 and n3 fundamental bands of BF2OH was performed, using FTS spectra recorded in Wuppertal.
The parameters for the 61, 71, 81 and 91 states as well as those of the 41 and 92 interacting states were redetermined, accounting for the resonances predicted by the ab initio calculations
New attempt to determine a semi-experimental structure

11. Congested spectrum: at 3700 cm-1 the Doppler line width is large)
The n1 band: very partial analysis:
Existence of several vibration rotation resonances ???

12. The n2 band: weakly perturbed
The n3 band: highly perturbed

13. Hamiltonian matrix for 71, 61, 91 and 81 in 2004

14. Hamiltonian matrix for 71, 61, 91 and 81 : this work

15. Ab initio equilibrium structure (B. O
Ab initio equilibrium structure (B.O.): confirmation of Breidung et al (2004)
In Breidung et al (2004) the ab initio equilibrium structure has been optimized with the coupled cluster method with single and double excitations and a perturbative treatment of connected triples, CCSD(T), with the correlation-consistent polarized valence n-tuple- basis sets (cc-pVnZ with n = 3, 4).
To estimate its precision, we repeated the optimization process. Conclusion: an accurate structure is obtained when the used basis set is large enough.
re(BFcis) = pm, re(BFtrans) = pm, re(BO) = pm, re(OH) = 95.74pm, angle(FBF) = °, angle(FcisBO) = °, angle(BOH) = °.

16. Anharmonic force field (Breidung et al. (2004)
… was calculated in Breidung et al. (2004) at the CCSD(T)_AE/TZ2Pf level of theory.
These parameters are of excellent quality. Indeed, there are
good agreements experimental  calculated values for:
The fundamental wavenumbers (including for n1, n2 & n3)
The centrifugal distortion constants

17. Rovibrational corrections: accounting (yes) or non accounting (no) from the vibration – rotation resonances

18. Semiexperimental structure
No isotopic substitution available for F
B atom is very close to the center of mass: (11B  10B) does not give any information)
On the other hand, (HD) leads to an axis switching effect$
Semiexperimental equilibrium inertial defect (in uÅ2)
$Demaison, Csaszar, Margulès, & Rudolph, J. of Phys Chem. J. Phys. Chem. A 115, p14078 (2011)

19. Conclusion
The first high resolution investigation of the n1, n2 and n3 fundamental bands of BF2OH was performed, using FTS spectra recorded in Wuppertal.
The parameters for the 61, 71, 81 and 91 states as well as those of the 41 and 92 interacting states were redetermined, accounting from the resonances predicted by the ab initio calculations
It was found that the ab initio a rovibrational corrections are more accurate than the experimental ones and can be used for the determination of the semi-experimental structure.

20. Detailed view of the hybrid (A- and B-type) n3 band