Theoretical study of Group 14 C+(2PJ)-RG and Si +(2PJ)-RG complexes (RG = He –Xe) William D. Tuttle, Rebecca L. Thorington, Larry A. Viehland and Timothy G. Wright ISMS 2017, Clusters/Complexes, RH02 June 22nd 2017

Why C+-RG and Si+-RG? Extension of work on M+-RG complexes from Groups 1, 2, 11, 12 and 13. Generating accurate interatomic potentials for use in calculation of ion transport data, useful for reaction kinetics involving ions. C+-He proposed as a cooling mechanism for C+ in the interstellar medium.1 Si+ ions of atmospheric importance; presence in upper atmosphere from meteoroids, important in understanding their rapid depletion with altitude.2 1N. Toshima, J. Phys. Soc. Jpn. 38, 1464 (1975). 2J. M. C. Plane et al., J. Geophys. Res. Atmos. 121, 3718 (2016).

Computational methodology RCCSD(T) interaction potentials arising from the non-SO terms and SO levels correlating with the C+,Si+(2PJ)-RG(1S0) asymptote computed in MOLPRO. Counterpoise-corrected at over 80 internuclear separations from short- to long-R. aug-cc-pwCVXZ (X=Q,5) basis sets for all atoms (except He, aug-cc-pVXZ), extrapolated to basis set limit. ECPs for Kr, Xe. CP-corrected interaction energies used as unperturbed eigenvalues of the Breit- Pauli SO matrix for SO-inclusive potentials.

C+-He : An illustrative example 2Σ+ 2Π

C+-He : An illustrative example 2Σ1/2+ 2Π3/2 2Π1/2

C+-He : An illustrative example Let’s look at some trends in Re, De, ωe and k!

2Πnon-SO

What about the influence of the SO effect?

2Π1/2 and 2Π3/2

What about the influence of the SO effect? Hund’s case (a): expected asymptotic 2PJ splitting is ~3/2 the molecular 2ΠΩ splitting (all below values in cm-1) C+-He C+-Ne C+-Ar Experiment Asymptotic splitting 61.2 63.42 Predicted Hund’s case (a) splitting at Re 40.8 Splitting at Re 41.3 41.4 59.8 (Re split./pred.)*100 101% 102% 147% Si+-He Si+-Ne Si+-Ar 261.7 287.24 174.5 187.0 183.5 178.0 107% 105%

What about the influence of the SO effect? Hund’s case (a): expected asymptotic 2PJ splitting is ~3/2 the molecular 2ΠΩ splitting (all below values in cm-1) C+-He C+-Ne C+-Ar C+-Kr C+-Xe Asymptotic splitting 61.2 Predicted Hund’s case (a) splitting at Re 40.8 Splitting at Re 41.3 41.4 59.8 162.8 450.3 (Re split./pred.)*100 101% 102% 147% 400% 1104% Si+-He Si+-Ne Si+-Ar 257.3 261.7 171.5 174.5 187.0 183.5 178.0 109% 105% RG C+ Charge transfer?

MRCI/aug-cc-pwCVQZ calculations (non-CP corrected, no SO effect) to compare to CCSD(T)/aug-cc-pwCVQZ potentials for the Ar, Kr and Xe complexes. ECPs for Kr, Xe. 2Π C+-Ar C+-Kr C+-Xe CCSD(T)/QZ MRCI/QZ Re / Å 2.003 1.999 2.079 2.082 2.206 2.215 De / cm-1 7876 8025 11772 12043 17059 17417 ωe / cm-1 408 413 433 435 447 445 k / cm-1 91 93 116 117 130 128 2Σ+ C+-Ar C+-Kr C+-Xe CCSD(T)/QZ MRCI/QZ Re / Å 3.009 2.997 2.912 2.910 2.803 2.797 De / cm-1 902 1006 1544 1703 3452 3783 ωe / cm-1 116 121 142 147 218 223 k / cm-1 7 8 13 31 32

Evidence of charge transfer from MRCI coefficients? Atom Ionisation energy / eV C 11.260 Si 8.1517 He 24.587 Ne 21.565 Ar 15.760 Kr 14.000 Xe 12.130 Atom Atom+(2PJ) splitting / cm-1 C 63.42 Si 287.24 He - Ne 780.42 Ar 1431.58 Kr 5370.10 Xe 10537.01 Ionisation energy approaching carbon down the RG series RG+ atomic splitting increasing significantly down RG series

Summary We have calculated accurate CCSD(T)/EBS interaction potentials for C+(2PJ)-RG(1S0) (RG = He – Xe) and Si+(2PJ)-RG(1S0) (RG = He – Ar). The influence of the spin-orbit interaction on the spectroscopic constants (and calculated ion transport properties) has been investigated. Significant deviations from Hund’s case (a) molecular spin-orbit splitting behaviour have been attributed to charge transfer in the heavier C+-RG species.

Future work Continuation to the heavier Si+-RG (RG = Kr, Xe) species to investigate charge transfer in those cases. Heavier Group 14 cations, where the SO splitting will be larger. Ion transport calculations (Larry Viehland) using these potentials, some of which is already published, alongside the spectroscopic constants.3,4 3William D. Tuttle, Rebecca L. Thorington, Larry A. Viehland and Timothy G. Wright, Mol. Phys., 113, 3767 (2015). 4William D. Tuttle, Rebecca L. Thorington, Larry A. Viehland and Timothy G. Wright, Mol. Phys., 115, 437 (2017).

Acknowledgements Thanks for your attention! Professor Timothy G. Wright Professor Larry A. Viehland Rebecca L. Thorington Dr Adrian M. Gardner Thanks for your attention! University of Nottingham HPC facility

2Σ+non-SO

2Σ+1/2

2Σ+1/2 Big influence on Re for Si+-RG complexes; due to proximity of 2Sig+ minimum to the 2Pi potential; interaction between 2Sig+1/2 and 2Pi1/2 serves to reduce bond length in the 2Sig+1/2 level, increasing interactions so higher De/k and higher ωe accompany this. Note that although this also mixes some 2Sig+ character into the 2Pi1/2 level, the 2Pi minimum is significantly separated from the 2Sig+1/2 potential, so this mixing is lessened near Re. The levels are further apart in the C+ complex due to the greater dissociation energies.