Chemical Reactions at 0.4 Kelvin Paul L. Stiles, Jeremy M. Merritt, Gary Douberly and Roger E. Miller Department of Chemistry University of North Carolina Chapel Hill, North Carolina 27599

Superfluid Helium Droplet Spectroscopy Solvent-Solute Interactions –CO 2 vs N 2 O rotational constants –Q-branches for linear molecules –IR-IR Double Resonance IR spectra of weakly bound complexesIR spectra of weakly bound complexes –(H 2 O) 6 –HCN linear chains –Entrance/Exit channel radical complexes –Clusters –Biomolecules

…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

HCN-Ag Pendular Scan Low HCN Pressure (1.5 x torr) Large Droplets (N ave > Moderate HCN Pressure (4 x torr) Moderate Droplets (N ave = 5000) HCN(HCN) 2 (HCN) 3 (HCN) 4 HCN-Ag HCN (HCN) 2 HCN-Ag HCN-Ag 2

HCN-Ag V 0 = cm -1 B = cm -1 D = 9 x cm -1 HCN-Ag Field Free Spectrum MP2 Calculations HCN/ G** Ag/Stuttgart RSC ECP B = cm -1 V 0 = 3305 cm -1 B gas /B he = 2.1 HCN-Cu V 0 = cm - 1 B = cm -1

 = 4.45 D 5 scan average Zero Field 1 scan 760 V/cm HCN-Ag Dipole Measurements See: RG10 HCN-Na MP2 Calculations HCN/ G** Ag/Stuttgart RSC ECP  = 4.63 D

Me-HX Insertion Reaction + Compare HF-Mg and HF-Al Systems

Mg-HF Calculations MP2/ G(3df,3pd) R HF = Å R MgH = Å B = cm -1 µ = D D e = -200 cm -1 V o = cm -1

HF-Mg x Pendular Spectra Mg-(HF) 2 Mg-HF

Mg-HF Zero Field and Stark Spectra  " = 2.2 D  ' = 2.6 D 9.64 KV/cm MP2/ G(3df,3pd) B = cm -1 µ = D v o = cm -1

Mg-HF-HF A = 0.3 cm -1 (B+C)/2 = cm -1 B gas /B He = 1.9 v 2 = cm -1  v 2 = 240 cm -1  = 3.2 D  v 1 = 154 cm -1 (R=0.924 Å)  v 2 = 230 cm -1 (R=0.926 Å)  = D A = cm -1 (B+C)/2 = cm -1 MP2/ G(3df,3pd) v2v2 v1v1

Al-HF: Our first candidate for photo-induced chemistry R HF =0.93 Å R HF =1.12 Å R HF =0.917 Å 0 -20, ,

B'' = cm -1 B' = cm -1 D = 1.8 x cm -1 v 0 = cm -1  v = cm -1  '' = 4.40 D  ' = 4.73 D KV/cm Stark Spectrum Al-HF Field Free Spectrum

Al-HF Calculations HOMO LUMO Basis SetR HF R HAl   HF  (D) G** G(3df,3pd) aug-cc-pvtz MP2 B = cm -1 Experiment B'' = cm -1  = cm -1  '' = 4.40 D

Al-HF x Pressure Dependencies

Basis SetB  HF  G** Al-HF-HF MP2 Calculations G**  1 = 173  2 = Unreacted Insertion Basis SetB  HF  Experiment B'' = cm -1  = cm -1  '' = 4.40 D

Conclusions 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