Spectra, Structures, and Dynamics of Weakly Bound Clusters from

Dimers to Nonamers

Wolfgang Jäger

Department of Chemistry, University of Alberta

Potential Energy Curves for H-Cl and Kr-Xe

Significance of van der Waals Interactions

Significance, continued …

Fourier Transform Microwave Spectrometer

Frequency range: 4 – 26 GHz (ca. 0.1 – 1 cm-1)

microwave cavity

nozzle

Fourier Transform Microwave Spectrometer

Outline for Remainder of Talk

• large amplitude motions in van der Waals complexes

• three-body effects in ternary and quaternary clusters

• successive micro-solvation of molecules with helium atoms

Ne-Ethylene in its Principal Inertial Axis System

Energy Level Diagram of Ne-trans-C2D2H2

(Out-of-Plane Motion)

Energy Level Diagram of Ne-trans-C2D2H2

(In-Plane Motion)

RGN-NH3 Complexes

Ne, Ar,a Kr NH3 Ne, Ar NH3 Ne, Ar NH3

15NH3 15NH3 15NH3

ND3 ND3 ND3

ND2H ND2H ND2HNDH2 NDH2 NDH2

a Ar-NH3, Ar-15NH3 by D. D. Nelson Jr. et al., JCP 85, 512 (1986); E. Zwart et al., JCP 95, 793 (1991); and many others.

J=4-3 Transitions of Deuterated Ar3-Ammonia

Ammonia internal rotation in RGN-NH3 clusters

14N nuclear quadrupole coupling constants in MHz

14N nuclear quadrupole coupling constant in free ammonia: =-4.0898 MHz

M. D. Marshall and J. S. Muenter, JMS 85, 322 (1981).

Three-Body Interactions

Three-body interactions

crystal structures of solid rare gases

face-centered cubic

(observed)hexagonal close-packed

(predicted using pairwise additivity)

NeAr

Ne2Ar

NeAr2

Ne3Ar

Ne2Ar2

NeAr3

Pure Rare Gas Clusters

Survey Scan with Ne/Ar Sample Gas Mixture

Transitions JKaKc = 202-101 of Ne2Ar

Rotational Energy Level DiagramsNe2Ar NeAr2

Comparison with Theoretical Calculations

Rotational

ConstantExperiment

pairwise

additive

pairwise +

AT term

A (MHz) 4724.1(8) 4742.30 4730.61

B (MHz) 2484.64(6) 2488.88 2486.92

C (MHz) 1597.88(6) 1592.57 1590.09

References:

1. Ernesti & Hutson, JCP 103, 3386 (1995).

2. Aziz & Slaman, Chem. Phys. 130, 187 (1989). Ne-Ne PES ~ viscosity data & high energy total cross sections

3. Barrow & Aziz, JCP 89, 6189 (1988). Ne-Ar PES ~ low energy total cross section data & low temperature second virial coefficients & room temperature diffusion coefficients & high energy total cross sections modified (scaled re) to fit MW data [JCP 102, 1181 (1995)].

Helium – Molecule Complexes

very weak interactions

high zero point energy spectra sample significant portion of PES attractive systems for ab initio calculations

relevant wrt spectroscopy of doped helium droplets

possibility to measure Hen-molecule systems?

S. Grebenev, J. P. Toennies, and A. F. Vilesov, Science 279, 2083 (1998).

Helium Nanodroplet Isolation Spectroscopy (Background)

Grebenev, Toennies, Vilesov, Science 279, 2083 (1998).

Helium Nanodroplet Isolation Spectroscopy (more Background)

Grebenev, Toennies, Vilesov, Science 279, 2083 (1998).

He-OCS in its Principal Inertial Axes System

Measured Rotational Transitions of He-OCS Is o to p o m er H e-O C S H e -O C 34S H e-O 13C S H e -O C 33SJ ' - J" νobs νob s νobs F'- F" νobs K a' , K c' K a" , K c" 1 0 ,1 - 0 0 ,0 9 1 6 1 . 8 1 2 0 a 8 9 5 8 .4 2 4 4 9 1 4 9 . 1 9 0 0 0 .5 -1 . 5 9 0 6 3 . 2 5 6 6 2 .5 -1 . 5 9 0 5 8 . 4 8 2 1 1 .5 -1 . 5 9 0 5 2 . 5 0 8 0

1 1 ,0 - 1 0 ,1 9 4 8 0 . 3 4 7 0 a 9 5 1 5 .6 5 4 0 9 4 4 8 . 8 0 0 3 1 .5 -2 . 5 9 4 9 9 . 9 7 3 5 0 .5 -1 . 5 9 4 9 9 . 4 0 1 6 2 .5 -2 . 5 9 4 9 6 . 3 4 1 2

1 1 ,1 - 0 0 ,0 1 6 8 4 1 . 2 6 8 0 1 6 7 4 6 .4 0 3 7 1 6 7 9 8 . 0 2 9 5 1 .5 -1 . 5 1 6 7 9 4 . 2 7 1 9 2 .5 -1 . 5 1 6 7 9 1 . 9 5 9 4 0 .5 -1 . 5 1 6 7 9 0 . 11 0 1

1 1 ,0 - 1 1 ,1 1 8 0 0 . 8 9 3 0 a - - 2 1 ,1 - 2 1 ,2 5 3 8 6 . 5 2 4 0 a - - 2 0 ,2 - 1 0 ,1 1 8 0 2 9 . 2 8 4 0 a 1 7 6 4 8 .0 8 5 6 1 8 0 0 3 . 6 3 9 8 1 .5 -1 . 5 1 7 8 3 8 . 3 6 7 6 3 .5 -2 . 5 1 7 8 3 4 . 1 0 9 4 2 .5 -1 . 5 1 7 8 3 4 . 0 8 3 8 0 .5 -0 . 5 1 7 8 3 3 . 6 1 7 3 2 .5 -2 . 5 1 7 8 2 8 . 1 0 8 2 1 .5 -0 . 5 1 7 8 2 7 . 6 1 9 9a K . H ig g in s a n d W . K lem p ere r , J . C h em . P h y s . 11 0 , 1 3 8 3 (1 9 9 9 ) .

J ' - J" νobs νob s νobs F'- F" νobs K a' , K c' K a" , K c"

He2-OCS in its Principal Inertial Axes System

JKaKc=101-000 Transitions of He2-OCS

Multidimensional Assignment Procedure

a) infrared predictions

b) sample conditions (pressure, temperature)

c) double resonance experiments

d) consistency of isotopic data

e) spectral fits

Effect of Nozzle Cooling on Cluster Formation

He6-OCS, J=3-2 at 11176.83 MHz, 0.01% OCS in He at 20.4 atm100 averaging cycles

nozzle at room temperatureS/N ~ 2

nozzle at dry ice temperature (-78.5 C)S/N ~ 40

Double Resonance Spectrometer

Double Resonance Spectrometer (Schematics)

Double Resonance Experiments on He6-OCS

signal: J-3-2, 11176.83 MHzpump: J=2-1, 7588.75 MHz20 averaging cycles

pump power(continuous)

off

-3 dBm

3 dBm

Vibrational Frequency Shifts of HeN-OCS Clusters

experimental valuesTang et al., Science, accepted.

values from Whaley and co-workers, JCP 115, 10225 (2001).

Moment-of-Inertia Shifts of Isotopomers

Proposed Structure of He8-OCS

Spectroscopic Constants of HeN-OCS ClustersMolecule B D

Free OCS 6081.59 1.31x10-5

He-OCS 13208.57

5504.18 4582.80

3661.42

0.950

He2-OCS 5803.39

4546.34 3782.81

3019.28

---

He3-OCS 3104.57 5.11

He4-OCS 2591.95 0.881

He5-OCS 2225.15 0.234

He6-OCS 1910.49 2.60

He7-OCS 1682.98 1.29

He8-OCS 1447.73 2.00

OCS in 4He droplet

(N~10,000)

2194.5(90) 11.4(3)

Rotational Constants of HeN-OCS Clusters

Potential Energy Surface of He-N2O

CCSD(T) level of theory, aug-cc-pVDZ basis set

Bound State Calculations

Transition Experiment Bound Difference

101 - 000 18560.5 MHz 18435.1 MHz 0.68 %

111 - 000 19743.3 MHz 19704.6 MHz 0.20 %

110 - 111 6295.0 MHz 6222.1 MHz 1.16 %

110 - 101 7477.5 MHz 7491.5 MHz -0.19 %

220 - 221 5035.0 MHz

211 - 212 18465.7 MHz

202 - 111 30342.8 MHz

211 - 110 30657.1 MHz

202 - 101 31612.3 MHz

211 - 110 42900.7 MHz

Wavefunction of Ground State

Wavefunctions of 1st and 2nd Excited States

J=1-0 Spectrum of He5-N2O

He6-N2O in its Principal Inertial Axes System

AcknowledgementsDr. Yunjie Xu (H31)Dr. Aiko Huckauf

Dean CourtDr. Yaqian Liu (H19)Dr. Jennifer van Wijngaarden (H15)Dr. Silas Ngari

Kai Brendel (H30)Hans OsthoffWendy Topic

Tobias KlemmerJames Song

Mike GerryBob McKellarPN Roy

NSERCASRACIPI