ENERGY LEVELS OF THE NITRATE RADICAL BELOW 2000 CM-1

Christopher S. Simmons, Takatoshi Ichino and John F. Stanton Molecular Spectroscopy Symposium, June 2012

Thanks to:NSF, DOE, Welch FoundationDan Neumark

Overview:

1. Qualitative vibronic coupling Hamiltonian results

2. Construction of quantitative vibronic coupling Hamiltonian

3. A rat's nest of states

4. Comparison of level positions with experiment

5. A truly ab initio simulation of the photodetachment spectrum of NO3-

Reminder about why NO3 is so complicated...

Before 2009-Qualitative Vibronic Hamiltonians

Used linear vibronic coupling KDC Hamiltonian of Mayer et al.Semiquantitative at best, much empiricism in constructionEngineered to fit aspects of nitrate PES

Described other spectra well, too. Suggested that it contains the essential physics.

but ...

Experiments have been unsuccessful* in observing v3

between 900-1100 cm-1, the region suggested.

A variational (Born-Oppenheimer) calculation suggeststhat v3 is extremely weak

This can be understood by a destructive interference effect between the intrinsic (diabatic) vibrational transitionmoment and an electronic contribution due to the strongX/B mixing (also seen in p-benzoquinone)

JFS Mol. Phys. 107, 1059 (2009).

2009-present: A new era for vibronic Hamiltonians

Challenging example for this new technology

Electronic structure calculations done at EOMIP-CCSDT with a large atomic natural orbital basis (computational aspects of getting this done constituted the bulk of a PhD thesis)

Diabatic coupling constants calculated with new ``quasidiabatic” CC model

Treatment of the JT splitting in the B state on the symmetry properties of the potential provided fodder for some nontrivial algebraic analysis

Quantum numbers: Domains of Sensibility

Quantum numbers: Domains of Sensibility

Forget it

Level PositionCalculated Observed Error369 365 +4 Kawaguchi777 758 +19 Neumark1069 1057 +12 Neumark1152 1173 -21 Jacox1424 1413 +11 Kawaguchi1494 1492 +2 Hirota157916421769 1774 -5 Jacox1845 1831 +14 Neumark1931 1927 +4 Hirota

Accuracy of e' energy levels from Hamiltonian

First Spectroscopic Application of the Hamiltonian:

The ab initio simulation of the nitrate PES

What do we mean by a truly "ab initio" simulation?

Hamiltonian (potential energy surfaces, coupling) fromquantum chemistry calculations

Relative cross sections (A2' and E') from theory

Calculation of cross sections with EOM-CC theory

Krylov: Dyson orbitals (Feynman-Dyson amplitudes)Recent work: Stieltjes imaging and Dyson orbitals (T. Ichino MI11)

A. Weaver, D.W. Arnold, S.E. Bradforth and D.M. Neumark J. Chem. Phys. 94, 1740 (1991)

origin

Experimental photodetachment spectrum

C.S. Simmons, T. Ichino and J.F. Stanton, submitted to JPC Lett

origin

Ab initio photodetachment simulation

a2' symmetry

e' symmetry

origin

origin

Closer inspection of the "v1" feature reveals ...

... that is should be called the "v3" feature!!!!!!!!!

Conclusions

Quantitative vibronic Hamiltonian gives excellent agreementwith known e' level positions in NO3

Assignment of quantum numbers becomes problematic above1500 cm-1

In conjunction with calculated cross sections, experimental photodetachment spectrum of nitrate reproduced almostquantitatively

There IS (!!!!) an e' level at about 1065 cm-1 that is best called "v3"and this feature is the dominant one underlying the second-strongestband in the experimental PES spectrum of NO3 anion

Nodal structure of 1492 cm-1 level is not consistent with it being a fundamental vibration

hopeless