1. RF16: Photogeneration of, and Efficient Collisional Energy Transfer from, Vibrationally Excited Hydrogen Isocyanide (HNC) Michael J. Wilhelm 1,#, Jonathan M. Smith 2, Matthew Nikow 1, and Hai-Lung Dai 2 1. Department of Chemistry, University of Pennsylvania, Philadelphia PA, 19104 2. Department of Chemistry, Temple University, Philadelphia PA, 19122 # Current Address: Department of Chemistry, Temple University, Philadelphia PA, 19122 17,000 5,000 12,000 68 th Annual OSU ISMS Columbus, OH June 20, 2013

2. R.D. Brown, Nature 270, 39 (1977); W.M. Irvine, Nature 383, 418 (1996); W.M. Irvine, Nature 393, 547 (1998) (Hale-Bopp) J(4-3) Lines: HNC (dashed) HCNx0.25 (solid) Hydrogen Isocyanide (HNC) Hale-Bopp 17,000 5,000 12,0002.1eV 1.5eV 0.6eV B.L. Lan and J.M. Bowman, J. Chem. Phys. 101, 8564 (1994).

3. UV Photolysis of VCN Following counter fragments: [HCN, HNC]  [H 2 CC:, HCCH] (HNC : HCN) = (0.3 : 1) Clean source of excited HNC (i.e., no spectral overlap). Collisional Deactivation: HNC + Rg

4. Time-Resolved IR Emission Spectroscopy LPX 200 ( =193 nm, t=50 ns, P≤50 mJ/cm 2 pulse) Figure Credit: David Osborn, Combustion Research Facility, Sandia National Labs, Livermore, CA 94551 (http://public.ca.sandia.gov/crf/viewArticle.php?cid=300008)

5. Step-Scan: Acquisition and Analysis Time-Resolved Series of Interferograms Reaction repeated for each mirror position,  i (+averaging) Full time signal measured at each  i. FT M.J. Wilhelm et al., J. Chem. Phys. 130, 044307 (2009). 193 nm Photolysis of VCN

6. A. Maki et al., J. Mol. Spec. 26, 47 (2001) [E ≤ ZPE + 6,000 cm -1 ] Ro-Vibrational Energy Levels: (Maki’s fit model) Modeling HNC Emission Selection Rules, Intensity, &tc: Calculated Vibrational Manifold (HNC)

7. Calculated HNC Spectral Basis Set (for fitting) Energy / 1000 cm -1 Frequency / cm -1

8. Fit Spectra: Determination of P j (t) Time- & Energy-dependent population distribution Energy-dependent spectral basis set Population Distribution: Vibrational Temperature HNC + Ar

9. Collisional Deactivation of HNC PTS Study - D. A. Blank, et al., J. Chem. Phys. 108, 5784 (1998) Time  Z Rg (collision #): (1:1) comparison between Rg Nascent E in (extrapolation) agrees with PTS 1 study. Well behaved reduced mass trend (  E: He  Ar  Kr  Xe). For a Rg collider, |  E| remarkably efficient!!

10. Order of magnitude more efficient! Comparative VET (e.g., HNC vs. NO 2 ) NO 2 + Rg He Xe Kr Ne Ar E. Sirota, M.S. Thesis, University of Pennsylvania (1997). Wilhelm, M.J.; Nikow, M; Smith, J.M.; and Dai, H.-L., J. Phys. Chem. Lett., 4, 23 (2013). Similar to: HCCO + Rg Attractive interactions?

11. Side Note: Deactivation of HNC 17,000 R-CN + h   HCN + (  )HNC + R’ If VET is sufficiently effective, nascent BR’s will be preserved..

12. Schwartz, Slawsky, and Herzfeld, J. Chem. Phys. 20, 1591 (1952). Tanczos, J. Chem. Phys. 25, 439 (1955).   A(  ) + M  A(  -1) + M Energy Distance DeDe (l,m,n) (l,m,n-1) (l,m-1,n) (l-1,m,n)  =-1 Wilhelm, M.J.; Nikow, M; Smith, J.M.; and Dai, H.-L., J. Phys. Chem. Lett., 4, 23 (2013). Modeling VET: Modified SSHT Theory D e <0 i.e., Attractive interactions enhance VET!

13. CCSD(T) / aug-cc-pVQZ  (3s3p2d2f1g) N C H 0o0o 90 o 180 o HCN + Rg R. R. Toczlowski, et al., J. Chem. Phys. 114, 851 (2001) Ab initio Interaction Potentials: H(CN) He Gh N C H (3s3p2d1f) HNC rr rr

14. SSH(T) Modeling Interaction Energy Comparison: SSH(T) vs. ab initio

15. Conclusions & Outlook Collisional deactivation of HNC is remarkably efficient: Ca. order of magnitude > comparable stable species ( i.e., >> 1cm -1 ). Attractive interactions, likely leading to formation of transient complex, aid in ET efficiency. Does efficient ET kinetically trap HNC? Would potentially preserve nascent H(CN) branching ratio. Variable ratio ~ f(CN-precursor identity & B.R.) Would be of interest to examine deactivation with ISM abundant species (e.g., H 2 ), and/or traditionally more efficient quenchers.

16. U.S. Department of Energy Grant # DEFG 02-86ER 134584 Funding Acknowledgements Dr. Jianqiang Ma UPenn, Dept. of Chemistry