Presentation is loading. Please wait.

Presentation is loading. Please wait.

Understanding Complex Spectral Signatures of Embedded Excess Protons in Molecular Scaffolds Andrew F. DeBlase Advisor: Mark A. Johnson 68 th Internatinal.

Similar presentations


Presentation on theme: "Understanding Complex Spectral Signatures of Embedded Excess Protons in Molecular Scaffolds Andrew F. DeBlase Advisor: Mark A. Johnson 68 th Internatinal."— Presentation transcript:

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 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 Cyclic ionic hydrogen bond x8 ν OH ν sp B3LYP/ G** scaled by above 2000 cm 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

5 Dramatic Change in Complexity as ΔPA is Decreased 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 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 Photon Energy (cm -1 ) Where’s NH the Bending Fundamental? 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 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 + ? Blob: Fewer discrete states: Photon Energy (cm -1 )

11 Can we sharpen the blob by reducing the DOS? Density of States (states/cm -1 ) Photon Energy (cm -1 ) 26,000 1,125, Introducing deprotonated oxalic acid…

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

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

14 Calculated Intensity/Predissociation Yield x4 Harmonic x4 Anharmonic 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= θ θ θ θ = 0 θ < 0 θ > 0

17 neutral anion laser energy Kinetic energy of ejected e¯ Binding energy 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 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 Photon Energy (cm -1 ) Predissociation Yield/Calculated Intensity Captures qualitative breadth quite well!


Download ppt "Understanding Complex Spectral Signatures of Embedded Excess Protons in Molecular Scaffolds Andrew F. DeBlase Advisor: Mark A. Johnson 68 th Internatinal."

Similar presentations


Ads by Google