Download presentation

Presentation is loading. Please wait.

Published byLeonard Leavenworth Modified about 1 year ago

1
Understanding Complex Spectral Signatures of Embedded Excess Protons in Molecular Scaffolds Andrew F. DeBlase Advisor: Mark A. Johnson 68 th Internatinal Symposium on Molecular Spectroscopy The Ohio State University: June 17, 2013

2
Previously … Charged hydrogen bonds show distinct spectral features. Roscioli et. al. Science 2007 Ar-predissociation 1000 15002000250030003500 Photon Energy (cm -1 ) Stoyanov and Reed J. Phys. Chem. A 2006 Room temperature FTIR

3
Not Always Simple! Chris Leavitt Leavitt et. al. J. Am. Soc. Mass Spectrom. 2011 Cyclic ionic hydrogen bond x8 ν OH ν sp B3LYP/6-311++G** scaled by 0.967 above 2000 cm -1 1200160020002400280032003600 Photon Energy (cm -1 )

4
Isolate the Cyclic Intramolecular Proton Bond ΔPA (kJ∙mol -1 ) ≈ 150 ≈ 190 ≈ 340 Prof. Tom Lectka: JHU R ( Å ) R 2.763 2.634

5
Dramatic Change in Complexity as ΔPA is Decreased 27002800290030003100320033003400 Photon Energy (cm -1 ) × 10 One sharp NH fundamental Weak CH stretches ν NH × 10 ν NH ν CH

6
Dramatic Change in Complexity as ΔPA is Decreased 27002800290030003100320033003400 Photon Energy (cm -1 ) × 10 One sharp NH fundamental Weak CH stretches ν NH × 10 ν NH ν CH All these features disappear when NH is replaced by ND DeBlase, et. al. J. Chem. Phys. In Press 2×Bend+stretch interactions?

7
15002000250030003500 Photon Energy (cm -1 ) Where’s NH the Bending Fundamental? 0 0.2 0.4 0.6 0.8 1.0 PHPH + Multiple possibilities for Fermi resonances 2 × 1500 = 3000 cm -1 Middle of the action Prediss. Yield, Calc. Int.

8
Theory Take 1: Bright State – Doorway State Model Couples bright states (i.e. fundamentals) to doorway states (i.e. 2×v i or v i + v j ) -Use 3 rd derivatives in potential to compute off-diagonal elements e.g. Overtone with ψ NH = ψ 1 and ψ overtone = ψ 2

9
180020002200240026002800300032003400 Photon Energy (cm -1 ) Predissociation Yield, Calculated Intensity 2×ν ND ip 2×ν ND oop 2×ν NH oop ν NH ν ND Seems to recover the complexity! Energy of NH(D) fundamental in initial matrix calculated using 2 nd order perturbation theory

10
How well does this method work with GlyGlyH + ? 22002400260028003000 Blob: Fewer discrete states: Photon Energy (cm -1 )

11
Can we sharpen the blob by reducing the DOS? 12001600200024002800 0 200000 400000 600000 800000 1000000 1200000 Density of States (states/cm -1 ) Photon Energy (cm -1 ) 26,000 1,125,000 15 Introducing deprotonated oxalic acid…

12
Calculated Intensity/Predissociation Yield 1200160020002400280032003600 Photon Energy (cm -1 ) Harmonic

13
Calculated Intensity/Predissociation Yield x4 Harmonic 1200160020002400280032003600 Photon Energy (cm -1 )

14
Calculated Intensity/Predissociation Yield x4 Harmonic x4 Anharmonic 1200160020002400280032003600 Photon Energy (cm -1 ) ~

15
Where else have we seen broadening associated with H-bonding? JPC (2003) Asymmetric doubly ionic H-bonds STILL BROAD BANDS BELOW 50 K

16
ν OH,v=0 (ZPE) θ ν OH,v=1 ν OH,v’=1 E, cm -1 U BO (θ) Potential energy surface for heavy atom motion changes with excitation of OH stretch Robertson, et. al. J. Phys. Chem. A 2003 Myshakin, et. al. J. Phys. Chem. A 2003 x x x x x x x x ν OH = ν OH’ ν Rock, v=0 1 3 4 2 θ θ θ θ = 0 θ < 0 θ > 0

17
neutral anion laser energy Kinetic energy of ejected e¯ Binding energy 0.00.51.01.52.02.5 EKE (eV) Shifted curves yield image of ground state vibrational wavefunction in Franck-Condon amplitudes for vibrational excitation (reflection principle)

18
Proton Adiabatic Curves Direction of reaction coordinate: L. D. Jacobson (Tully Postdoc) Theory: Take 2

19
0 500 1000 1500 2000 2500 3000 3500 4000 -0.1-0.05 0.0 0.05 0.1 Reaction Coordinate ( Å ) Energy (cm -1 ) Shared proton vibration is responsive to the reaction coordinate

20
Acknowledgements Funding: NSF and DOE Mark: Keeping us well fed! Lectka group (JHU): synthesis Theory: Anne McCoy and Ken Jordan

21
Extra Slides

22
Theory: Take 2 Prof. Anne McCoy The Ohio State University Adiabatic separation of OH stretch (q OH ) and the other 3N-7 vibration degrees of freedom, leading to: Transition strength of the OH stretch: Using the linear approximation of the dipole moment: And normal mode basis: Ψ(q OH,q) ≈ ψ(q OH :q)χ(q) Randomly displace along each of the 3N-7 coordinates (within zero-point motion) and calculate the ν OH

23
160020002400280032003600 Photon Energy (cm -1 ) Predissociation Yield/Calculated Intensity Captures qualitative breadth quite well!

Similar presentations

© 2017 SlidePlayer.com Inc.

All rights reserved.

Ads by Google