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Full dimensional rovibrational variational calculations of the S1 state of C2H2 -or- “less is more less” P. Bryan Changala JILA, National Institute.

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Presentation on theme: "Full dimensional rovibrational variational calculations of the S1 state of C2H2 -or- “less is more less” P. Bryan Changala JILA, National Institute."— Presentation transcript:

1 Full dimensional rovibrational variational calculations of the S1 state of C2H2 -or- “less is more less” P. Bryan Changala JILA, National Institute of Standards and Technology and Department of Physics, University of Colorado, Boulder, CO Joshua H. Baraban Department of Chemistry, University of Colorado, Boulder, CO John F. Stanton Department of Chemistry, University of Texas, Austin, TX ISMS 70, UI Urbana-Champaign, IL, 2015

2 Outline Vibrational structure of S1 surface and cis-trans isomerization effects Revisit previous reduced dimension (4D) calculations Full dimensional (6D) treatment and method Compare 4D and 6D results

3 Cis-trans isomerization in the S1 state

4 Challenge 1: trans bending polyads
- + + - Darling-Dennison resonance and Coriolis coupling form bending polyads:

5 Challenge 2: isomerization “dip”

6 Challenge 3: tunneling K-staggerings
K-staggering in cis 3161 Merer et. al., J. Chem. Phys, 134, , 2011.

7 Old 4D calculation (“not bad”)
J. Chem. Phys. 140, E (cm-1) cis levels 21 Stretch-bend combinations 31 61 Pure stretch Pure Bn polyads 41

8 Hybrid global potential surface
High-quality 4D PES (bending+torsion+RCC) EOM-CCSDT/ANO1 Lower-quality 6D PES (add both rCH’s) EOM-CCSD/ANO1 Hybrid 6D global surface

9 Full dimensional basis representations
C H Re-phased rot. function Stretch DVR Legendre poly. Torsion Fourier basis Correct boundary conditions, symmetry adaptable, real matrix elements 6D DVR basis: PES is diagonal Complex tor-rot basis: KEO is simple, analytic Compute many times  Iterative Lanczos diagonalization

10

11 Reduced vs. full dim. frequencies
trans mode Exp (cm-1) 4D 6D hybrid sym. CH str, ν1 2880 --- 2712 CC stretch, ν2 1387 1396 sym. bend, ν3 1048 1071 1027 torsion, ν4 765 749 711 asym. CH str, ν5 2857 2693 asym. bend, ν6 768 774 741 trans B’s Exp. 6D calc A 13.057 12.370 B 1.1238 1.1425 C 1.0307 1.0295 Exp: 2670 ± 10 cm-1 4D: 2910 6D: 2750 Hybrid surface is bad! T0

12 Conclusions & ongoing work
Implemented exact 6D + rotation variational energies and wavefunctions on global S1 PES Low-level (CCSD) 6D hybrid extension of high-level (CCSDT) 4D surface performs quite poorly Currently constructing new high-level 6D surface Acknowledgements: NSF GRFP

13 K-staggerings in cis and trans levels
cis state Obs (cm-1 ) Calc 3161 +3.9 +1.6 62 -5 ± 1 -3.0 v = 0 --- +0.0(3) 63 -62 3162 +42 trans state Obs (cm-1 ) Calc 34 (0) 35 +6.3 -4.1 3461 +27 -19* 3462 -6.9 56 (-64*) *3D Minimally, need K = 0-2 measurements (for even/odd staggering) Ideally, want K = 0-4 (torsional staggering?, perturbations)

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