effects of multiple argon tagging in alkali metal m + h 2 oar n and m + d 2 oar n studied by irpd...
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Effects of Multiple Argon Tagging in Alkali Metal M+H2OArn and M+D2OArn studied by IRPD Spectroscopy
Christian van der Linde, Haochen Ke, and James M. Lisy
University of Illinois at Urbana-Champaign
ISMS 2014
RJ11
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Introduction
• Alkali-Metal ions are of great importance in many biological processes
• M+(H2O) are suited as modelfor microscopic solvation
• Uncertainty of internal energy of the gas phase cluster, depends on the composition of the cluster and the method of generation
M
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• Evaporatively cooled M+(H2O)Arn cluster
• Argon tagging: commonly one Ar atom• But sometimes more than one Ar atom necessary to have
sufficient fragmentation for M+(H2O) cluster (e.g. M = Cu)
M+(H2O)n≥4 250 – 350 KM+(H2O) > 500 KM+(H2O)Ar 100 – 200 K
Introduction
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Nd3+:YAG Laser (1064 nm)
Filament
Source
Detection Chamber
Differential Pumping Stages
Q1 Q2 Q3
Experimental Setup
LaserVision OPO/A
Ar/H2O
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Spectra | Na+H2OArn
• Symmetric Band – ΔK = 0– P/R Splitting
• Asymmetric Band – ΔK = ±1
• Spin Statistics– 1/3 odd/even
• Internal Rotation for n > 1
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• Analysis of K-States
– Asymmetric Band Origins
– A-Rotational Constant
– Internal Temperature
Spectra | Analysis
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• Decrease with increasing ion size and number of Ar
• T(D2O) < T(H2O)
Temperature | Trends
M+H2OArn
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• Shift to higher frequencies with increasing ion size and number of Ar
• Water is less disturbed with more Ar atoms in the cluster
Asym. Band Origins | Trends
H2O (3756 cm-1)M+H2OArn
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• Decrease with increasing ions size and number of Ar• Slight change in HOH angle and/or OH bond lengths
Rotational Constant | Trends
M+H2OArn
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Hindered Rotor | Analysis
• Some features are split and/or broad• Especially transitions involving K = 1 states
• Influence of a Rotational Barrier
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Can M+H2OAr1,2 cluster be described as 2-fold hindered Rotor?
• Torsional Oscillation vs. Free Rotation
Diagram from G. Herzberg, Infrared Spectra.
Hindered Rotor | Concept
M
ArAr
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Hindered Rotor | Energy Diagram
• K = 1 levels split for small barriers
• Higher levels do not split (significantly) for small barriers
• Population changes due to splitting of the levels
• Three Possibilities:
a) v0 splits
b) v1 and v0 split
c) v1 splits
Fre
e R
ota
tio
n
Tors
ion
al V
ibra
tion
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Hindered Rotor | Different Barriers
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Hindered Rotor | Different Barriers
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Hindered Rotor | 20cm-1 BarrierKNa
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• Trends were identified
• Same Trends for D2O
• A small rotational barrier of ~20 cm-1 in the v1 state can explain the splitting and broadening for most spectra
Summary
n Ar
1 2 3
Temperature
Band Origins
Rotational Constants
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James M. Lisy and Haochen Ke
Acknowledgement
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CHE11-24821
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Hindered Rotor | 20cm-1 BarrierRb Cs
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