A Combined Theoretical and Experimental Study of the HF+CN  F + HCN Reaction; The CN-HF Entrance channel complex Jeremy Merritt and Michael Heaven Department of Chemistry Emory University Atlanta, GA 30322

A Combined Theoretical and Experimental Study of the HF+CN  F + HCN Reaction; The CN-HF Entrance channel complex Department of Chemistry Emory University Atlanta, GA Jeremy Merritt and Michael Heaven

Motivation Weak van der waals forces can strongly influence dynamics Cl + HD; Roaming Hydrogen atom mechanism HX-CN has been suggested as being important in controlling the product state distributions observed in X+HCN scattering Multiple, asymptotically degenerate Potential energy surfaces can result in breakdown of the Born-Oppenheimer approximation Reaction dynamics at the quantum level 4 atom systems Photoinduced reaction of entrance channel complexes impact parameter averaging Aid in understanding future experimental results X, A, and B states of CN are convenient handles

A global picture

Ab initio Calculations Start with rigid monomers constrained to a common plane = C s   [0.1, 180.1, 20.0]   [0.1, 360.1, 20.0] R  [10.0, 6.0, 5.0, 4.5, 4.0, 3.75, 3.5, 3.25, 3.0, 2.75, 2.5 Å] r HF = År CN = Å F C N   R  r HF r CN Performed using MOLPRO (gas phase values) CN Basis set = Aug-cc-pVDZ+{332} Methodology 1)RHF for 1A’ state 2)4SA-CASSCF(7,8) 3)MRCI(7,7) 4)Counter-Poise Correction using Davidson Energies 5) Correct for size consistency (20 Å)

CN – HF; What to expect CN 22 2*2* 33 xx yy 33 x*x* y*y* X 2  +

CN – HF; What to expect CN 22 2*2* 33 xx yy 33 x*x* y*y* B 2  +

CN – HF; What to expect CN 22 2*2* 33 xx yy 33 x*x* y*y* A 2  22 A’ A” For Non-linear geometries 4SA-CASSCF(7,8) 1A”, 3A’

Tests on CN monomer MRCIExp. X 2  + r e (Å) A 2  T e (cm -1 ) A 2  r e (Å) B 2  + T e (cm -1 ) B 2  + r e (Å)

F C N   R = 3.5 Å X 2  + B 2  + A 2  A” A’ FH--CN FH--NC HF--NC HF--CN

F C N   R = 4.0 Å X 2  + B 2  + A 2  A” A’ FH--CN FH--NC HF--NC HF--CN

Theta = 0 degrees F C N  R

F C N  R Theta = 180 degrees

Dihedral cut F CN     R = 3.5 Å 

Stationary points FH---NC FH---CN HF---NC HF---CN X 2  + B 2  + A 2  D e = 1200 cm -1 R e = 3.4 Å D e = 1000 cm -1 R e = 3.4 Å repulsive D e = 1570 cm -1 R e = 3.6 Å D e = 1300 cm -1 R e = 3.6 Å R e = 3.8 Å D e = 330 cm -1 Small isomerization barrier Small isomerization barrier D e = 330 cm -1 R e = 3.8 Å Bent?

Why the geometry flip-flop?

Collinear FH-CN Reaction Path HF bonding orbital (F 2P z ) was included into the active space  H exp = 4046 cm -1  H = 3125 cm -1

Summary and Conclusions HF+CN PES is rich Bound-Bound (Bound-Free) transitions expected for A-X (B-X) excitation of FH--NC Onset of continuum would accurately probe ground state binding energy ~7300 cm -1 barrier to reaction; should be ammenable to jet cooling Zewail type experiments?