1. Evidence for Photolytic Production of Cyclic-N 3 Dr. Petros Samartzis, Dr. Nils Hansen, Yuanyuan Ji, Alec M. Wodtke Dept. of Chemistry and Biochemistry UCSB, Santa Barbara CA 93106 Air Force Office of Scientific Research

2. Outline Background  Poly-nitrogen allotropes are rare… …ring structures even more so. Three experiments provide evidence for photochemical production of cyclic N 3  Velocity Map Imaging Thermochemistry of all molecules made from one Cl atom and three N atoms.  Photofragmentation translational spectroscopy Primary and Secondary decomposition pathways resulting from ClN 3 photolysis  VUV synchrotron photoionization based photofragmentation translational spectroscopy Two photo-ionization thresholds for N 3

3. Some background on all Nitrogen Chemistry …especially rings

4. The Nitrogen atom as a chemical building block N is iso-electronic with CH If benzene,Then, why not Hexa-azabenzene

5. Basic Problem of Stability with all-Nitrogen Ring Allotropes

6. Theory on Cyclic Nitrogen Allotropes T. J. Lee et al., J. Chem. Phys. 94, 1215-1221 (1991). W. J. Lauderdale et al., J. Phys. Chem. 96, 1173-1178 (1992). D. R. Yarkony, J. Am. Chem. Soc. 114, 5406-5411 (1992). R. Klein et al., Chem. Pap.-Chem. Zvesti 47, 143-148 (1993). K. M. Dunn et al., J. Chem. Phys. 102, 4904-4908 (1995). M. N. Glukhovtsev et al., Inorg. Chem. 35, 7124-7133 (1996). A. A. Korkin et al., J. Phys. Chem. 100, 5702-5714 (1996). M. T. Nguyen et al., Chem. Berichte 129, 1157-1159 (1996). J. Wasilewski, J. Chem. Phys. 105, 10969-10982 (1996). A. Larson et al., J. Chem. Soc.-Faraday Trans. 93, 2963-2966 (1997). M. L. Leininger et al., J. Phys. Chem. A 101, 4460-4464 (1997). M. Bittererova et al., J. Phys. Chem. A 104, 11999-12005 (2000). M. Bittererova et al., Chem. Phys. Lett. 340, 597-603 (2001). M. Bittererova et al., Chem. Phys. Lett. 347, 220-228 (2001). T. J. Lee et al., Chem. Phys. Lett. 345, 295-302 (2001). H. Ostmark et al., J. Raman Spectrosc. 32, 195-199 (2001). M. Tobita et al., J. Phys. Chem. A 105, 4107-4113 (2001). M. Bittererova et al., J. Chem. Phys. 116, 9740-9748 (2002). T. J. Lee et al., Chem. Phys. Lett. 357, 319-325 (2002).

7. Many interesting allotropes have been predicted by theory Hexa-azabenzene 212 kcal/mole Hexa-aza Dewar-benzene 244 kcal/mol Hexa-aza Prismane 323 kcal/mol Hexa-aza bicyclopropenyl 245 kcal/mol Hexa-aza diazide 189 kcal/mol Motoi Tobita and Rodney J. Bartlett J. Phys. Chem. A 2001, 105, 4107-4113 Stable ? ? ?

8. N8N8 N 10

9. Poly-Nitrogen Chemistry Limited number of allotropes belonging to this family have been synthesized and identified. N≡N N=N=N  N=N=N  0.33 0.22  0.11 +1

10. N 5 + Synthesis proved by IR and crystal structures.

11. N 5  Identified in fragmentation of electrospray ionization mass spectra.

12. Tetra-azahedrane (tetrazete): The search continues Obeys the octet rule. Dissociation to 2N 2 releases 760 kJ/mol. (Interesting HEDM candidate) Must proceed over 250 kJ/mole barrier to be spin- allowed Spin-forbidden channels have lower barriers… Produce excited electronic state products

13. Matrix Isolation Nitrogen discharges quenched on cold surface IR spectra recorded Compared to theoretical predictions Very recent work from Radziszewski appears promising

14. Theoretical simulation of isotopic IR spectrum of T d - N 4

15. Cyclic-N 3 : the “simplest” all-Nitrogen ring allotrope and precursor to T d -N 4 C 2v Symmetry Bound by 1 eV if “spin conserved” @1 eV barrier to linearization precursor to tetra-azahedrane Bittererova, Östmark and Brinck, J. Chem. Phys. 116 9740 (2002)

16. Pseudo-rotation in cyclic N 3 Energy minimum exhibits C 2v symmetry Shallow barrier through to other isomers. Barrier lower than zero-point energy Molecule exhibits pseudo-rotation Photochemical angular distribution will be broadened All N-atoms are equally likely to leave Babikov, Morokuma, Zhang… several recent papers have appeared.

17. ׀׀׀׀ ++++ + 2B12B1 2A22A2 2B12B1 2B12B1 2A22A2 2A22A2 ׀ + ׀ + ׀ + ++++ ++++ ++++ ׀׀׀׀ ++++ +׀+׀ BO GBO Geometric Phase Effect Babikov et al., J. Chem. Phys., 121, (24), 22 December 2004

18. #1: BO A 1 1310 cm -1 #2: E 1364 cm -1 #3: E 1561 cm -1 Vibrational Wave-functions With and Without the Geometric Phase Effect #1: GPE, E, 1325cm -1 #2: GPE, A 1 1401 cm -1 #3: GPE, A 2, 1502 cm -1 Babikov et al., J. Chem. Phys., 121, (24), 22 December 2004

19. Cyclic-N 3 postulated as a Reaction Intermediate 15 N-Tracer Evidence Discounting the Occurrence of a Cyclic Azide Intermediate in the Reaction Between Nitrous-acid and Hydrazine, R. J. GOWLAND et al., J. Chem. Soc.-Dalton Trans., 797-799 (1992).

20. Cyclic N 3  postulated N 2 Matrix subjected to ion bombardment Infrared spectrum recorded. Comparison to theory  SCF level of theory

21. Up to now, no conclusive experimental evidence Surprisingly, no effort has been made to exploit UV photolysis to make this metastable compound.

22. Theoretical predictions about cyclic N 3 Zhang, Morokuma and Wodtke (in press)

23. Three experimental approaches Velocity Map Imaging  Thermochemistry of all molecules made from one Cl atom and three N atoms. Photofragmentation translational spectroscopy  Primary and Secondary decomposition pathways resulting from ClN 3 photolysis VUV synchrotron photoionization based photofragmentation translational spectroscopy  Two photo-ionization thresholds for N 3

24. Velocity Map imaging of Cl from ClN 3 → Cl+N 3 …thermochemistry of Cl/N/N/N

25. Velocity Map Ion Imaging

26. Inverse-Abel Transformation Inverse Abel-Transformation Using BASEX alla Reisler M. C. Escher  3D-Distribution  2D-Projection:  Cut through 3D-Distribution:

27. N 2 O + h  N 2 (X 1  g + ) + O ( 1 D 2 )  Velocity Map w/ centroidingw/o centroiding “Improved two-dimensional product imaging: The real-time ion-counting method”, Chang BY, Hoetzlein RC, Mueller JA, Geiser JD, Houston PL, RSI 69 (4): 1665-1670 APR 1998  ~  1 N 2 O Photodissociation “Photodissociation of N 2 O: J-dependent anisotropy revealed in N 2 photofragment images”, Neyer DW, Heck AJR, Chandler DW, JCP, 110 (7): 3411-3417 FEB 15 1999

28. N 2 O (0,0,0) N 2 O (0,1,0) Comparison to Cornell Experiments Santa Barbara machineCornell machine * * “Improved two-dimensional product imaging: The real-time ion-counting method”, Chang BY, Hoetzlein RC, Mueller JA, Geiser JD, Houston PL, RSI 69 (4): 1665-1670 APR 1998 Determines the N 2 -O bond energy within several cm -1

29. ClN 3 absorption spectrum 1A ”  1A ’ 3.1 eV 2A ’  1A ’ 5.1 eV 2A ”  1A ’ 5.6 eV Experimental Absorption Spectrum Theoretical calculations of Zhang and Morokuma Cl-atom N-atom N2N2

30. Experiments with 6 eV photons: Formation of N 2 ( J=68 ) + NCl(X 3  and a 1  ) Parallel transition:  P(a)/P(X) = 0.78/0.22 

31. Thermochemistry of ClN 3  N 2 + NCl Maximum release of translational energy provides accurate thermochemistry ClN 3  N 2 (X) +NCl:  E =  0.93eV ClN 3  N 2 (a) +NCl:  E = 0.22eV

32. Imaging of ClN 3 + 2 h  ClN 3  + e   NCl  + N 2 confirms this thermochemistry   =1.1 NCl 

33. Velocity Map Image of Cl from ClN 3  N 3 + Cl( 2 P 1/2 ) Symmetrized image Reconstructed v-map  Two components Internally cold linear N 3

34. D 0 (Cl-N 3 ) from Velocity Map Imaging E  is known from laser wavelength. E MAX is derived

35. Thermochemistry of the Cl/N/N/N Zero Kelvin Heats of Formation All heats of formation now known within  0.1 eV Predicted by Bittererova et al.

36. Velocity Map Image of Cl( 2 P 3/2 ) Bimodal energy distribution Angular Distributions parallel but not identical 80% of E ava in translation 45% of E ava in translation

37. Photofragmentation translation spectroscopy Establishing the decomposition pathways important in ClN 3 photolysis.

38. Photofragmentation Translational Spectroscopy Electron bombardment ionization of photofragments provides universal detection  With Ion fragmentation Detector is rotate-able to accept products recoiling at different angles,  TOF reflects laboratory speeds, from which we extract the c.m. frame translational energy release, P(E T )

39. NCl + observed, but weak! ClN 3 + h  → N 2 +NCl( 1  ) minor 60 0 E ava 75 kcal/mol in products of this reaction!  =  0.3

40. Cl + -TOF, 50 o : Cl + N 3 is dominant channel Consistent with VMI, bimodal TOF observed ClN 3 + h →  Lin-N 3 + Cl  HEF-N 3 + Cl ClN 3 + h →  NCl + N 2  NCl+ h → N+Cl 50 0  = 1.7  = 0.4

41. N 3 +, bimodal N 3 distribution ClN 3 + h →  lin-N 3 + Cl  HEF-N 3 + Cl Long-lived HEF N 3 50 0  = 1.7  = 0.4

42. Translational Energy Distributions of ClN 3 →Cl+ N 3 M 1 v 1 = M 2 v 2  Experiments at m/z=42 (N 3 + ) and m/z=35 (Cl + ) are fundamentally redundant.  Yet differences arise  Likely due to N 3 dissociation.

43. Wavelength Dependence VMI at 235 nm summed over Cl ( 2 P J ) PTS at 248 nm. Both Features shifted by change in photon energy.

44. N 2 +, unimolecular decomposition and photolysis of N 3 N 3 → N 2 + N( 4 S) N 3 → N 2 + N( 2 D) N 3 + h  → N 2 +N( 2 D) 30 0

45. N +, unimolecular decomposition and photolysis of N 3 N 3 → N 2 + N( 4 S) N 3 → N 2 + N( 2 D) N 3 + h  → N 2 +N( 2 D) 50 0

46. N 3 Secondary photodissociation Data fit by two models  lin-N 3 + h →N( 2 D)+N 2  HEF-N 3 + h →N( 2 D)+N 2 Evidence suggests the selective photo- dissociation of HEF- N 3 at 248 nm

47. Primary and Secondary dissociation channels of 248 nm photolysis of ClN 3 ClN 3 + h  → NCl+ N 2  NCl + h  → N + Cl ClN 3 → Cl+ N 3 (low energy form) ClN 3 → Cl+ N 3 (high energy form)  N 3 → N 2 + N( 4 S)  N 3 → N 2 + N( 2 D)  N 3 + h  → N 2 +N( 2 D)

48. VUV synchrotron photoionization based photofragmentation translational spectroscopy Two thresholds in photo-ionization for N 3

49. Experiment nearly unchanged Instead of electron impact ionization of photofragments We can use tunable VUV photons for near threshold ionization  Eliminate ion fragmentation  Measure ionization threshold

50. Cl + and N 3 + TOF Bimodal features seen again N 3 observed with much better S/N Two forms of N3 well resolved in the TOF distribution N3+N3+ Cl +

51. TOF spectra of N 3 vs. ionization photon energy White light continuum produces “below threshold ions” 11.07 eV ionization of “fast peak” matches literature value for linear N 3 New threshold ~10.6 eV

52. Two photoionization thresholds for N 3 produced in ClN 3 photolysis Tosi, 2004 Krylov & Babikov, 2005 John Dyke, 1982 LINEAR N 3 Experiment With Jim Jr-Min Lin at Hsinchu, NSRRC in Taiwan CYCLIC N 3 /N 3 + theory ● f ast channel  slow channel N 3 neutral TOF N 3 + photoionization yield

53. Conclusions UV photolysis of ClN 3 at 248 nm produces Cl and N 3 with 0.95 quantum yield. Primary and Secondary decomposition pathways have been mapped out Two energetic forms of N 3 seen, whose  H F ’s are in agreement with what is known for linear and cyclic N 3 VUV photoionization threshold data also in agreement with theoretical predictions for linear and cyclic N 3 If indeed we are seeing cyclic-N 3, it is long lived.

54. Acknowledgements Dr. Petros Samartzis, Dr. Nils Hansen, Yuanyuan Ji,  Dept. of Chemistry and Biochemistry, UCSB, Santa Barbara CA 93106 Dr. Jason Robinson, Niels Sveum Dan Neumark,  UC Berkeley Dr. Jim Jr-Min Lin, Tao-Tsung Ching, Chanchal Chadhuri, Shih-Huang Lee  National Synchrotron Radiation Research Center, Hsinchu 30077, Taiwan, Republic of China Air Force Office of Scientific Research National Science Foundation