Effects of Multiple Argon Tagging in Alkali Metal M + H 2 OAr n and M + D 2 OAr n studied by IRPD Spectroscopy Christian van der Linde, Haochen Ke, and James M. Lisy University of Illinois at Urbana-Champaign ISMS 2014 RJ11

Introduction Alkali-Metal ions are of great importance in many biological processes M + (H 2 O) are suited as model for microscopic solvation Uncertainty of internal energy of the gas phase cluster, depends on the composition of the cluster and the method of generation 2 M

Evaporatively cooled M + (H 2 O)Ar n cluster Argon tagging: commonly one Ar atom But sometimes more than one Ar atom necessary to have sufficient fragmentation for M + (H 2 O) cluster (e.g. M = Cu) M + (H 2 O) n≥4 250 – 350 K M + (H 2 O)> 500 K M + (H 2 O)Ar100 – 200 K Introduction 3

Nd 3+ :YAG Laser (1064 nm) Filament Source Detection Chamber Differential Pumping Stages Q1 Q2 Q3 Experimental Setup LaserVision OPO/A Ar/H 2 O 4

Spectra | Na + H 2 OAr n 5 Symmetric Band –ΔK = 0 –P/R Splitting Asymmetric Band –ΔK = ±1 Spin Statistics –1/3 odd/even Internal Rotation for n > 1

Analysis of K-States –Asymmetric Band Origins –A-Rotational Constant –Internal Temperature 6 Spectra | Analysis

Decrease with increasing ion size and number of Ar T(D 2 O) < T(H 2 O) Temperature | Trends M + H 2 OAr n 7

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 H 2 O (3756 cm -1 ) 8 M + H 2 OAr n

Decrease with increasing ions size and number of Ar Slight change in HOH angle and/or OH bond lengths Rotational Constant | Trends 9 M + H 2 OAr n

Hindered Rotor | Analysis Some features are split and/or broad Especially transitions involving K = 1 states 10 Influence of a Rotational Barrier

Can M + H 2 OAr 1,2 cluster be described as 2-fold hindered Rotor? Torsional Oscillation vs. Free Rotation Diagram from G. Herzberg, Infrared Spectra. Hindered Rotor | Concept 11 M Ar

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) v 0 splits b) v 1 and v 0 split c) v 1 splits Free Rotation Torsional Vibration 12

Hindered Rotor | Different Barriers 13

Hindered Rotor | Different Barriers 14

Hindered Rotor | 20cm -1 Barrier 15 KNa

Trends were identified Same Trends for D 2 O A small rotational barrier of ~20 cm -1 in the v 1 state can explain the splitting and broadening for most spectra Summary 16 n Ar 123 Temperature Band Origins Rotational Constants

James M. Lisy and Haochen Ke Acknowledgement 17 CHE

Hindered Rotor | 20cm -1 Barrier Rb 18 Cs

19