1. Vibronic Spectroscopy of Jet-Cooled 1,4-Phenylene Diisocyanide 6/21/11 1 DEEPALI N. MEHTA, ANNA K. GUTBERLET, AND TIMOTHY S. ZWIER 66 th International Symposium on Molecular Spectroscopy TG07 Department of Chemistry, Purdue University West Lafayette, IN 47907

2. Motivation 2 [1] Kemsley, J.,Chemical and Engineering News, 2007, 85, 11 [2] Raulin, F., Space Sci. Rev. 135, 2008, 37-48 Figure 1 1 : Schematic of reactions in Titan’s atmosphere. Titan is a model system for studies of primordial Earth 2 Titan’s chemistry occurs via ion and neutral pathways. 2

3. The formation of benzene (78 amu) has been investigated. 3 Compounds at 78 amu and greater, suggesting possibility benzene-based derivatives. 4 Motivation 3 [3] Wilson, E. H., and Atreya, S. K., J. Geophys. Res.-Planet, 2004, 109 [4] J. H. Waite, D. T. Young, T. E. Cravens, A. J. Coates, F. J. Crary, B. Magee, J. Westlake, Science, 2007, 316, 870-875 Figure 2 4 : Density as a function of mass, for compounds present in Titan’s atmosphere. Note the presence of mass 128. 128 amu

4. Motivation 4 Species such as HCN, HC 3 N, C 2 N 2, and NH 3 open up possibility of nitrogen containing benzene derivatives. 5 Interest in isocyanides (also called isonitriles) which contain the R-N≡C group. Spectroscopy of isonitriles is less well understood 1,4-phenylene diisocyanide (1,4- PDI, Figure 3) shares the same (nominal) mass as naphthalene (128 amu), and is an interesting candidate for spectroscopic investigation Figure 3: Structure of 1,4 phenylene diisocyanide [5] A. J. Trevitt, G. Boulay, C. A. Taatjes, D. L. Osborn, S. R. Leone, J. Phys. Chem. A, 2010, 114, 1749-1755 + -+ - C CN N

5. Motivation 5 34,255cm -1 35,120cm -1 865cm -1 [6] J. A. Stearns, T. S. Zwier, J. Phys. Chem. A, 2003, 10717-10724 [7] K. Fujita, T. Fujiwara, K. Matsunaga, F. Ono, A. Nakajima, H. Watanabe, T. Koguchi, I. Suzuka, H. Matsuzawa, S. Iwata, K. Kaya, J. Phys. Chem., 1992, 96, 10693-10697. ? para-Diethynylbenzene para-Dicyanobenzene 1,4-Phenylene Diisocyanide

6. Experimental 6 Collisional cooling to zero- point vibrational levels Sample entrained in high pressure backing gas Supersonic Expansion S0S0 Cooling Laser Induced Fluorescence UV laser (tuned) (S 0,v=0) A * (S n ) Detect total fluorescence PMT UV laser (fixed) Total fluorescence CCD Dispersed Fluorescence

7. Experimental 7 Laser Ports 2 Stage Ion Acceleration Einzel Lens Pulsed Valve MCP Time-of-Flight Tube Mass Gate Pulser 1C-R2PI Ionization continuum SnSn S0S0 2C-R2PI SnSn S0S0 Resonant 2 Photon Ionization (R2PI) Tuned Laser Fixed Laser Tuned Laser

8. Experimental 8 UV-UV Holeburning S0S0 SnSn 20 Hz Probe (Tuned) 10 Hz HB Δt = 200 ns Ionization continuum Δt = 50-200 ns Holeburn Laser (10Hz) Probe Laser (20Hz) Spectra collected using active baseline subtraction Wavenumbers (cm -1 ) Probe only Difference * Probe + Holeburn Lasers spatially overlapped but temporally separated

9. LIF Spectrum of 1,4-Phenylene Diisocyanide (PDI) 9 Origin at 35,566cm -1 S 0 -S 1 LIF excitation spectrum, spanning 35,000-40,500cm -1. The S 0 -S 1 electronic origin of 1,4-PDI has been identified as 35,566cm -1. Peaks marked * were anticipated to be due to other species.

10. Hole-burning Spectra 10 R2PI Hole-burning Vibronic transitions due to same ground state 000000 *

11. Dispersed Fluorescence of S 0 -S 1 Origin Band 11 Dispersed fluorescence of S 0 -S 1 electronic origin at 35,566cm -1.

12. Dispersed fluorescence of vibronically coupled mode 17 at 36,024cm -1. Inset within the graph is a visualization of normal mode 17, which has b 3g symmetry. ν 17 17 1 1 Δv=0 17 1 0 Δv=-1 17 1 2 Δv=+1 Dispersed Fluorescence of +458cm -1 Band 12

13. Vibronic Coupling and Tentative Assignments 13 Table 2. ExperimentalCalculatedSymmetry ν3ν3 16711679 agag ν5ν5 12041215 agag ν6ν6 823842 agag ν7ν7 393396 agag ν 11 403414 b 2g ν 12 187182 b 2g ν 15 13271347 b 3g ν 16 649662 b 3g ν 17 500508 b 3g ν 35 305303 b 3u ν 36 8384 b 3u Calculated frequencies provided as courtesy of Head- Gordon group, using Qchem with rimp2-cc-pvdz. Table 1. SymmetryOscillator Strength S1S1 B 2u 0.0015 S2S2 B 1u 0.6065 Excited state calculations using time dependent density functional theory were performed using Gaussian 09 with a b3lyp functional and 6-31+g(d) basis set B 2u × b 3g =B 1u

14. LIF Spectrum of 1,4-Phenylene Diisocyanide (PDI) 14 Origin at 35,566cm -1 S 0 -S 1 LIF excitation spectrum, spanning 35,000-40,500cm -1. The S 0 -S 1 electronic origin of 1,4-PDI has been identified as 35,566cm -1. 17 1 0 000000

15. Identification of S 0 -S 2 15 S 0 -S 2 LIF excitation spectrum, spanning 40,500-44,100cm -1, approximately 6,100cm -1 above the S 0 -S 1 origin. R2PI LIF S 0 -S 2 origin

16. Dispersed Fluorescence from S 2 16 Dispersed fluorescence of S 0 -S 2 at 41,711 cm -1. The broadened emission near the S 0 -S 1 origin suggests a S 2  S 1 internal conversion, followed by fluorescence to the ground state. S0S0S0S0 S1S1S1S1 S2S2S2S2 Internal Conversion

17. Discussion: Comparison of Isoelectronic Species 17 865cm -1 34,255cm -1 35,120cm -1 para-Diethynylbenzene para-Dicyanobenzene [6] J. A. Stearns, T. S. Zwier, J. Phys. Chem. A, 2003, 10717-10724 [7] K. Fujita, T. Fujiwara, K. Matsunaga, F. Ono, A. Nakajima, H. Watanabe, T. Koguchi, I. Suzuka, H. Matsuzawa, S. Iwata, K. Kaya, J. Phys. Chem., 1992, 96, 10693-10697. 1,4-Phenylene Diisocyanide 35,566cm -1 466cm -1

18. 18 Monosubstituted BenzeneOrigin (cm -1 )Relative Absorption (cm -1 ) ethynylbenzene 8 358790 phenyl cyanide 8 36516637 phenyl isocyanide 8 36706827 Disubstituted Benzene (para)Origin (cm -1 )Relative Absorption (cm -1 ) para-diethynylbenzene 6 342550 para-dicyanobenzene 7 35120865 1,4-PDI (para-diisocyanobenzene)355661311 Summary A fluorescence excitation spectrum spanning the range 35,500-44,100 cm -1 (226.5-281.5 nm) has been recorded. The S 0 -S 1 origin was identified at 35,566cm -1, and the S 0 -S 2 origin was identified nearly 6,100 cm -1 above. Modes with b 3g symmetry exhibit strong vibronic coupling to nearby B 1u second excited state (S 2 ). [8] A. R. Muirhead, A. Hartford, Jr, K-T Hurang, J. R. Lombardi, J. Chem. Phys., 1972, 56, 4385-4393

19. Future Directions 19 Spectroscopy  Photoionization efficiency scans  More complete analysis of vibronic structure in S 1 manifold Photochemical studies  Long-lived excited states as in phenylacetylene?  Study NC to CN isomerization

20. Acknowledgements 20 Professor Timothy S. Zwier The Zwier Group Josh Sebree (TB08, TD11) Evan Buchanan (WI10) Zachary Davis James Redwine Jacob Dean (RG11) Nathanael Kidwell (WI11) Joseph Korn Di Zhang