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

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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