A Theoretical Search for an Electronic Spectrum of the He–BeO Complex Adrian M. Gardner and Michael C. Heaven 69th International Symposium on Molecular Spectroscopy University of Illinois at Urbana-Champaign June 20th 2014

Introduction to RG Containing Complexes RG–X interactions are predominately “physical” in origin. However covalency has been found in some RG–X complexes, largely those involving krypton and xeon, such as the Kr–CuF complex.1 1.Thomas et al. J. Am. Chem. Soc., 2004, 126 (4), 1235-1246. RG αRGD / Å3 Ionization Energy / eV He 0.205 24.6 Ne 0.396 21.6 Ar 1.64 15.8 Kr 2.48 14.0 Xe 4.04 12.1

HeCCHe2+ → He + HeCC2+ De ≈ 10000 cm-1 Strong He–X Bonds Frenking and coworkers investigated many helium containing species.2,3 HeCCHe2+ → He + HeCC2+ De ≈ 10000 cm-1 They concluded that a strong He–X bond could form if: there is a high charge on X; X has a suitable s- or σ-hole. As a result, the He–BeO complex was investigated. He–BeO → He + BeO De ≈ 1700 cm-1 Subsequent calculations determine De ≈ 1900 cm-1.4 2. Koch et al., J. Am. Chem. Soc., 1987, 109, 5917-5934. 3. Koch et al., Chem. Phys. Lett., 1986, 132, 330-333. 4. Hapka et al., J. Phys. Chem. A, 2013, 117, 6657-6663.

He–BeO There have been several theoretical investigations which have focused on the mechanism of bonding within the He–BeO complex.4,5,6 The unanimous conclusion is that the He–Be interaction is largely non-covalent. Figure taken from Ref. 4. Term energies and geometries of bound vibrational levels of the ground electronic state have been determined.4 Only one study has investigated electronically excited states of the He–BeO complex and concluded these states were only weakly bound.7 Matrix isolation has resulted in the observance of Ar–, Kr –, and Xe–BeO complexes.8 The He–BeO complex has yet to be observed experimentally. 4. Hapka et al., J. Phys. Chem. A, 2013, 117, 6657-6663. 7. Heaven et al., Chem. Phys. Lett., 2011, 506, 1-14. 5. Frenking et al., J. Am. Chem. Soc., 1988, 110, 8007-8016. 8. Thompson and Andrews, J. Am. Chem. Soc., 1994, 116, 423-424 6. Zou et al., J. Phys. Chem. A, 2013, 117, 207-212.

He–BeO Why study the He–BeO complex experimentally? Beryllium containing species are particularly challenging species to probe theoretically. Many species have been suggested based results of theoretical studies which contain strong helium bonds, but none have been observed experimentally. Why electronic spectroscopy? The X1Σ+ state of He–BeO has a rotational constant of ~0.6 cm-1. Allows the dissociation energy of the ground and excited states to be determined. M* + RG D0ʹ (M–RG)* T0 M + RG D0ʹʹ M–RG

He–BeO Why study the He–BeO complex experimentally? Beryllium containing species are particularly challenging species to probe theoretically. Many species have been suggested based results of theoretical studies which contain strong helium bonds, but none have been observed experimentally. Why electronic spectroscopy? The X1Σ+ state of He–BeO has a rotational constant of ~0.6 cm-1. Allows the dissociation energy of the ground and excited states to be determined. M* + RG (M–RG)* DL M + RG D0ʹʹ M–RG

RG–BeO With increasing RG atomic number: the RG–BeO bond would be expected to become stronger. possibility for covalent bonding is increased. De calculated at the CCSD(T)/awCV5Z level RG αRGD / Å3 De / cm-1 He 0.205 1880 (1780) Ne 0.396 1830 (1750) Ar 1.64 (4140)

He–BeO The dominant electron configuration of the X1Σ+ state of BeO is 1σ22σ23σ24σ21π4. ...4σ21π35σ1 ← …4σ21π4 A1Π ...4σ11π45σ1 ← …4σ21π4 B1Σ+

Excited Electronic States of BeO Calculations were performed at the CASSCF+MRCI+Q level. Active space consisted of 1s, 2s and 2p atomic orbitals of Be and O, and 1s of He. The aug-cc-pwCVTZ basis sets were employed for Be and O and aug-cc-pVTZ for He. All calculations were performed using MOLPRO. Electronically excited states of the BeO molecule have been the subject of a previous investigation.10 States with a …4σ21π32π1 electronic configuration were reported lying > 40000 cm-1 above the ground state. 10. Buenker et al., J. Chem. Phys., 2007, 126, 104305

Excited Electronic States of BeO Dominant electron configurations: X1Σ+ …4σ21π4 A1Π ...4σ21π35σ1 B1Σ+ ...4σ11π45σ1 C1∆ and D1Σ- …4σ21π32π1 CASSCF/MRCI(12/10)+Q/awCVTZ

Excited Electronic States of He–BeO CASSCF/MRCI(14/11)+Q/awCVTZ

Excited Electronic States of He–BeO (Aʹ/Aʹʹ) (Aʹ) CASSCF/MRCI(14/11)+Q/awCVTZ

Excited Electronic States of He–BeO HeBeO+(X2Π) ≈

Excited Electronic States of He–BeO He(1S) + BeO+(X2Π) ≈

Excited Electronic States of He–BeO

Excited Electronic States of He–BeS CASSCF/MRCI(10/9)+Q/awCVDZ

Excited Electronic States of He–BeS (Aʹ/Aʹʹ) (Aʹ) (Aʹ/Aʹʹ) CASSCF/MRCI(10/9)+Q/awCVDZ

Excited Electronic States of BeO Dominant electronic configurations: E1Π ...4σ11π42π1 F1Π ...4σ21π36σ1 CASSCF/MRCI(12/10)+Q/awCVTZ

Excited Electronic States of He–BeO CASSCF/MRCI(14/11)+Q/awCVTZ

Conclusions Future Work Electronically excited states of the He–BeO complex have been calculated. The C1∆ state is crossed by the B1Σ+ state. Two other electronic states (E1Π and F1Π) have been found which demonstrate strong He–BeO bonds. Future Work 2-dimensional potential energy surfaces are being calculated. Extend these calculations to include the heavier RG complexes. Increase the basis set size employed. Attempt the proposed experiments!!