jake a. tan and jer-lai kuo institute of atomic and molecular sciences academia sinica taipei,...
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Jake A. Tan and Jer-Lai KuoInstitute of Atomic and Molecular Sciences
Academia SinicaTaipei, Taiwan
International Symposium on Molecular Spectroscopy69th Meeting – University of Illinois Urbana-Champaign
Unfolding the Quantum Nature of Proton Bound Symmetric Dimer of (MeOH)2H+:
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Outline
IntroductionMotivationStratagemResults
(MeOH)2H+
Isotope substitution Ar Messenger Effect
Take Home Messages
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Intermolecular Proton Bond (IPB)
• Refers to the interaction between the electronegative atoms of two closed-shell molecules sandwiching an excess proton (H+).
Intermolecular Proton Bond
(IPB)
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What is the relationship between
ΔPA and νIPB?
How about for ΔPA =0?
νIPB
ΔPA
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Coupling between IPB and flanking group motions?
ν IPB
ν ip, sym O-C-O
ν op, sym O-C-O
ν IPB
ν op, free O-H bend
ν op, C-O str
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(Me2O)2H+ Exp.
(Me2O)2H+ Calc. (Harm.)
(Me2O)2D+ Exp.
(Me2O)2D+ Calc. (Harm.)
Same case for (MeOH)2H+!
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Outline
IntroductionMotivationStratagemResults
(MeOH)2H+
Isotope substitution Ar Messenger Effect
Take Home Messages
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Motivation
• Most of the experimental literatures do speculate the coupling between IPB and flanking group motions.
– A theoretical study can shed light on the extent of these interactions.
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Stratagem
Quantum Chemistry
Basis Set
Normal Mode Dimensionality
B3LYP/6-311+G(d,p)
Up to 4D
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StratagemDimensionality Aspect
• Insights from One-Dimensional Treatment– The effective scan range
• Insights from Two-Dimensional Treatment – Modes that couple
• Insights from Higher-Dimensional Treatment– Cumulative effect of other modes on IPB stretch
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StrategyMethod of Finite Difference:• For a one-dimensional problem we have:
Where, 𝜇𝑚𝑜𝑑𝑒 1 is the reduced mass for normal mode 1 𝑞𝑚𝑜𝑑𝑒 1 is the coordinate associated with normal mode 1
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Outline
IntroductionMotivationStratagemResults
(MeOH)2H+
Isotope substitution Ar Messenger Effect
Take Home Messages
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(MeOH)2H+
O-O Stretch IPB Stretch
Free O-H BendingOut phase C-O stretch
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(MeOH)2H+
Assignment may be easy with Normal Mode Coordinates
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(MeOH)2H+
F ig. 1 Mixing of the fi rst exci ted states of IPB st re tching mode w i th out phase C-O st re tching mode (upper row ) and f ree O-H bending ( low er row ). Due to a near ly 45° t i l t ing of nodal planes, i t is possible to make an assignment f rom the w avef unc t ions topology. T he co lored contour refe rs to the corresponding PES and the color map values are in te rms of atomic uni t s.
Assignment may NOT easy with Normal Mode Coordinates
IPB Stretch will be based on the larger oscillator strength
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(MeOH)2H+
ν O-O, str ν op, C-O, strν op, O-H bend, str
1D
2D
3D
4D
ν IPB, str
Harmonic
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(MeOD)2D+
ν O-O, str
ν op, C-O, str
ν op, O-D bend ν IPB, str
1D
2D
3D
4D
Harmonic
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Outline
IntroductionMotivationStratagemResults
(MeOH)2H+
Isotope substitution Ar Messenger Effect
Take Home Messages
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Motivation
• It is well known that Ar tagging do affect the stretching frequency of free O-H.
• How about the IPB bond? • Is Ar really innocent?
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Ar(MeOH)2H+
ν op, C-O, str
ν op, O-H bend ν O-O, strν IPB, str
1D
2D
3D
4D
Harmonic
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Outline
IntroductionMotivationStratagemResults
(MeOH)2H+
Isotope substitution Ar Messenger Effect
Take Home Messages
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Take Home Messages• Intermolecular Proton Bond (IPB) indeed could strongly couple with
some of the flanking group motions.
• Our isotope studies w/ (MeOD)2D+ predicts that coupling will be lessened and a clean spectrum is obtained. Opens for expt. validation
• Argon tagging perturbs the modes of (MeOH)2H+
– IPB is sensitive with the environment– Perhaps studies tagged by He, Ne and other messengers can help us to
understand IPB’s sensitivity with the environment.• Isotope substitution, messenger tagging are useful weapons in resolving the
nature of IPB’s coupling.
In agreement w/ MAJ In addition
ν op, C-O, str ν O-O, str
ν op, O-H bend
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Jer-Lai Kuo Kaito Takahashi