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A global ab initio -based potential energy surface for of H 5 + , vibrational zero-point, and reaction dynamics of H 3 + + HD

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A global ab initio-based potential energy

surface for of H5+, vibrational zero-point,

and reaction dynamics of H3+ + HD

JMB, Bas Braams, Zhen Xie,

Emory University,

NationalScience Foundation, Office of Naval Research

- Deuterium fraction
- Spectroscopy
- Thermochemistry
- Reaction rates

D. Gerlich, E. Herbst, and E. Roueff, Planet Space Sci. 50, 1275 (2002)

D. Gerlich, S. Schlemmer, , Planet. Space Science 50, 1287(2002)

Challenges for Theoretical Chemistry

- Potential energy surfaces
- Spectroscopy
- Thermochemistry/ZPE
- Dynamics

Ab initio electronic structure

R. Prosmiti, P. Villarreal, G. Delgado-barrio, (2001,2003) - DIM-fit PES

H. Müller and W. Kutzelnigg, PCCP (2000) - CC-R12, stationary pts, De

Y. Yamaguchi, J. F. Gaw, R. B. Remington, H. F. Schaefer III, (1987) -

Dynamics

I.Stich, D.Marx, M.Parinello, T.Terakura (1997) - PI/DFT

W.P.Kraemer, V.Spirko, and O.Bludsk (1994) - Red Dim vibrations

G. Moyano and M. Collins, (2003) - “GROW” QCT k(T)

Stationary Points

H5+ Potential Energy Surface (2005)

- Ca 105ab initio energies [CCSD(T)/aug-cc-pVTZ]
- Fit with a polynomial basis the is invariant wrt
- any permutation of the 5 H atoms.
- Many-body representation that gives the
- fragments H3+ and H2
- Use a switching function to describe
- long-range electrostatic interaction.

- Z. Xie, B. J. Braams, and J. M. Bowman J. Chem. Phys. 122, 224307 (2005).

H5+ Potential Energy Surface (2005)

a Muller &Kutzelnigg, b Prosmiti et al. eMoyano & Collins

Spectroscopy and Thermochemistry

HD + H3+ [H4D+]H2+ + H2D+

Thermochemistry - get the ZPEs accurately. HO?

Spectroscopy - detect reactant and products and maybe stabilizedH4D+

M. Okumura, L. I. Yeh, and Y. T. Lee (1988) - H5+

H5+ H3+ + H2 , D0= 6.8±0.3 kcal/mol

- The most accurate De = 8.58 kcal/mol
- The present PES De = 8.30 kcal/mol

- Using HO ZPEs PES gets D0 = 5.57 kcal/mol
- (Not in good agreement with experiment)

From the DMC ZPEs we get D0 = 6.33±.03 kcal/mol

Exp* = 6.8±0.3 (HO = 5.57)

*Exp1 = 6.6 ±0.3,Exp2 = 7.0 ±0.1

Present Deis low by 0.28 compared

to most accurate ab intio value

So, our estimate would be 6.6 kcal/mol

H4D+ H3+ + HD D0 = 6.63 kcal/mol

H2D+ + H2 D0 = 6.37 kcal/mol

H3+ + HD H2D+ + H2 , E = -90 cm-1 (-0.26 kcal/mol)

HD + H3+ H2+ + H2D+

Ecoll= 95 K

( H’D + H3+)

Statistical expectations

Always form a “collision complex” - Langevin xsection

Classically 60% to H2 + H2D+, P(b) = 0.6

and40% to H’D+ H3+ withP(b) = 0.3 for H’≠H

P(b) = 0.1 H’=H

Reaction Cross Sections Vs. Collision Energy

Ecoll= 95 K

- Global PES done - PI, dissociates, VLR ad hoc
- DMC calcs of ZPEs and Do
- QCT calculations of xsection and rate constant
- (Not statistical, mostly proton hopping)

To Do

- Quantum calculations of vibrational energies
- and IR spectrum. (This is feasible with Multimode.)
- Quantum calculation of the rate constant. (This is
- very hard to do in full dimensionality.)

CH5+

Like H5+ there are 5! equivalent

Minima, saddle points.

Fit to 36173 CCSD(T)/aug-cc-pVTZ

Does CH5+ have a structure?

- Oka’s unassigned spectrum
- Marx and Parinello
- Schaefer, Scheiner, Schlyer
- Klopper and Kutzelnigg

A. Brown, B. J. Braams, K. Christoffel, Z. Jin,

and J. M. Bowman, J. Chem. Phys., 2003, 119, 8790. - fit and MD spectrum

A. Brown, A. B. McCoy, B. J. Braams, Z. Jin,

and J. M. Bowman, J. Chem. Phys., 2004, 121, 4105. - fit and DMC

A.B. McCoy, B .J. Braams, A. Brown

et al., J. Phys. Chem. A, 2004, 108, 4991. - DMC isotopmers

Close to statistical and independent of initial geometry

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