Chemical Reactions at 0.4 KelvinChemical Reactions at 0.4 Kelvin

Paul L. StilesPaul L. Stiles, Jeremy M. Merritt, Gary Douberly , Jeremy M. Merritt, Gary Douberly and Roger E. Millerand Roger E. Miller

Department of ChemistryDepartment of Chemistry

University of North CarolinaUniversity of North Carolina

Chapel Hill, North Carolina 27599Chapel Hill, North Carolina 27599

Superfluid Helium Droplet Superfluid Helium Droplet SpectroscopySpectroscopy

• Solvent-Solute Interactions– CO2 vs N2O rotational

constants– Q-branches for linear

molecules– IR-IR Double

Resonance

• IR spectra of weakly IR spectra of weakly bound complexesbound complexes– (H(H22O)O)66

– HCN linear chainsHCN linear chains

– Entrance/Exit channel Entrance/Exit channel radical complexesradical complexes

– ClustersClusters

– BiomoleculesBiomolecules

……but what about “Chemistry”?but what about “Chemistry”?

• One of our long-term goals was to observe chemical reactions inside helium droplets– Metal catalyzed reactions

– Organic Radical reactions

• See TJ07 Jeremy Merritt

3302 3304 3306 3308 3310 3312

Wavenumbers (cm-1)

3302 3304 3306 3308 3310 3312

Wavenumbers (cm-1)

HCN-Ag Pendular ScanHCN-Ag Pendular Scan

Low HCN Pressure (1.5 x 10-6 torr)Large Droplets (Nave> 10000

Moderate HCN Pressure (4 x 10-6 torr)Moderate Droplets (Nave= 5000)

HCN(HCN)2

(HCN)3

(HCN)4

HCN-Ag

HCN

(HCN)2

HCN-Ag

HCN-Ag2

HCN-AgV0 = 3304.92 cm-1

B = 0.0315 cm-1

D = 9 x 10-5 cm-1

HCN-Ag Field Free SpectrumHCN-Ag Field Free Spectrum

MP2 CalculationsHCN/6-311++G**Ag/Stuttgart RSC

ECP

B = 0.0661 cm-1

V0 = 3305 cm-1

Bgas/Bhe = 2.1

HCN-CuV0 = 3297.33 cm-1

B = 0.043 cm-1

3304.6 3304.8 3305.0 3305.2 3305.4

Wavenumbers (cm-1)

= 4.45 D

3304.6 3304.8 3305.0 3305.2 3305.4

Wavenumbers (cm-1)

5 scan averageZero Field

1 scan760 V/cm

HCN-Ag Dipole MeasurementsHCN-Ag Dipole Measurements

See: RG10 HCN-Na

MP2 Calculations

HCN/6-311++G**

Ag/Stuttgart RSC ECP

= 4.63 D

Me-HX Insertion ReactionMe-HX Insertion Reaction

+

Compare HF-Mg and HF-Al SystemsCompare HF-Mg and HF-Al Systems

Mg-HF CalculationsMg-HF CalculationsMP2/6-311++G(3df,3pd)MP2/6-311++G(3df,3pd)

RHF = 0.91998 ÅRMgH = 3.1245 Å

B = 0.09566 cm-1

µ = 2.7921 DDe = -200 cm-1

Vo = 3874.6 cm-1

3700 3750 3800 3850 3900

Wavenumbers (cm-1)

HF-HF

Mg2-HF

Mgx-HF

HF-MgHF-Mgxx Pendular Spectra Pendular Spectra

Mg-(HF)2 Mg-HF

Mg-HF Zero Field and Stark SpectraMg-HF Zero Field and Stark Spectra

3876.9 3877.2 3877.5 3877.8 3878.1 3878.4

Wavenumbers (cm-1)

" = 2.2 D' = 2.6 D

9.64 KV/cm

MP2/6-311++G(3df,3pd)MP2/6-311++G(3df,3pd)B = 0.09566 cm-1

µ = 2.7921 Dvo = 3874.6 cm-1

3719.7 3720.0 3720.3 3720.6 3720.9

Wavenumbers (cm-1)

Mg-HF-HFMg-HF-HF

3719.7 3720.0 3720.3 3720.6 3720.9

Wavenumbers (cm-1)

A = 0.3 cm-1

(B+C)/2 = 0.026 cm-1

Bgas/BHe= 1.9

v2 = 3719.1 cm-1

v2 = 240 cm-1

= 3.2 D

v1 = 154 cm-1 (R=0.924 Å)v2 = 230 cm-1 (R=0.926 Å)= 4.554 DA = 0.372 cm-1

(B+C)/2 = 0.0497 cm-1

MP2/6-311++G(3df,3pd)

v2 v1

Al-HF: Our first candidate for Al-HF: Our first candidate for photo-induced chemistryphoto-induced chemistry

RHF=0.93 Å

RHF=1.12 Å

RHF=0.917 Å

0

-20,000

-1600

+70

-21,000

-600

3753.00 3753.25 3753.50 3753.75 3754.00

Wavenumber (cm-1)

B'' = 0.03090 cm-1

B' = 0.03017 cm-1

D = 1.8 x 10-5 cm-1

v0 = 3753.51 cm-1

v = 205.7 cm-1

'' = 4.40 D

'' = 4.40 D' = 4.73 D

2.518 KV/cm

Stark Spectrum

Al-HFAl-HFField Free SpectrumField Free Spectrum

Al-HF CalculationsAl-HF Calculations

HOMO

LUMO

Basis Set RHF RHAl HF (D)

6-311++G** 0.9283 2.799 293 3.021

6-311++G(3df,3pd) 0.9314 2.706 365 2.908

aug-cc-pvtz 0.9380 2.673 389 2.924

MP2

B = 0.107 cm-1

ExperimentB'' = 0.03090 cm-1

= 205.7 cm-1

'' = 4.40 D

Al-HFAl-HFxx Pressure Dependencies Pressure Dependencies

0.0 5.0x10-6 1.0x10-5 1.5x10-5 2.0x10-5 2.5x10-5 3.0x10-5

18 K

17 K

20 K

19 K

HF Dimer HF

xAl

Pressure (Torr)

21 K

10,000

7200

5700

4600

3700

Average Droplet Size

Basis Set B HF

6-311++G** 0.0792 207 4.75

Al-HF-HF MP2 CalculationsAl-HF-HF MP2 Calculations

6-311++G** 0.04861= 173

2= 5124.96

Unreacted

Insertion

Basis Set B HF

6.2BB

He

gas

6.1BB

He

gas

ExperimentB'' = 0.03090 cm-1

= 205.7 cm-1

'' = 4.40 D

ConclusionsConclusions• HCN-Ag

– Nitrogen-bound linear rotor bound by dipole induced-dipole interactions

• Weaker interaction and smaller dipole than HCN-Cu

• Mg-HF– Assigned bands

• Hydrogen-bound binary complex• Hydrogen-bound Mg-(HF)2

• Al-HF– Only one band is seen from 4000 cm-1 to 3580 cm-1

– Band is associated with two HF molecules– We are forming the H-Al-F insertion product bound with an

additional HF molecule

Acknowledgments

• Funding– NSF

– Air Force Office for Scientific Research

• People– William K.Lewis– Myong Yong Choi– Travis Falconer– Mike Barrett– Mike Lindsey, Ph.D.– Alessandra Ferzoco– Peter Lake

• University of North Carolina, Chapel Hill