The exotic excited state behavior of 3-phenyl-2-propynenitrile KHADIJA JAWAD, CLAUDIA I. VIQUEZ, LYUDMILA SLIPCHENKO, AND TIMOTHY S. ZWIER 72nd International Symposium on Molecular Spectroscopy TB10 Department of Chemistry, Purdue University West Lafayette, IN 47906

Motivation Previous work on photochemical reaction between diacetylene and benzene yielded phenyldiacetylene Photochemical reaction between benzene and cyanoacetylene could produce PPN Spectroscopic signature of PPN important to confirm its production Assignments difficult to make due to confusion over the identity of the excited state(s) involved

Previous Work: R2PI Possible S0-S1 origin at 35,242 cm-1 Sharp peaks up to 37,000 cm-1 Broad absorptions similar to phenyldiacetylene above 37,000 cm-1 292 nm 208 nm

Experimental: Laser-Induced Fluorescence Laser Induced Fluorescence Chamber

LIF

Origin Dispersed Fluorescence Lacks a1 vibrational fundamentals Points to importance of vibronic coupling Prominent peaks can be assigned to b2 fundamentals b1 vibrations appear alongside corresponding b2 Possible coupling to S2 state 3601 b2 1101 a1 3501 b2 3701 b2 801 a1 1901 b1 2401 b1 1301 a1 1401 a1 3801 b2

Vibrations of C3N group appear in pairs: b1 and b2 Mode Symmetry  Experimental EOM-CCSD/cc-pVDZ ν (cm-1) b2 69 b1 75 192 3801 212 211 2401 356 362 1401 a1 379 366 a2 402 3701 482 489 502 524 3601 534 538 3501 627 630 659 1301 686 693 758 865 1901 939 933 969 981 1101 1008 1015

Vibrations involved in b1-b2 pairs n39 69cm-1 n26 75cm-1 n38 211cm-1 n25 192cm-1 n36 538cm-1 n22 524cm-1

LIF Revisited 35,242 cm-1 000 +472 ν37 +205 ν38 +115 +65 +186 +255

Dispersed Fluorescence Resonant fluorescence x3 False origins Δν=0 Franck-Condon factors Geometry similar between ground and excited state

How are b1 and b2 fundamentals gaining intensity in emission? Transition Symmetry Oscillator Strength S0 – S1 B2 0.003233 S0 – S2 A1 0.361093 S0 – S3 A2 0.000000 S0 – S4 Modeling of ν24 (b1) Strong vibronic coupling between excited states EOM-CCSD/cc-pVDZ Claudia I. Viquez MG10 −1.0 -0.5 0.0 0.5 1.0 1.5 2.0 Displacement

Conclusions and Future Work Ground and excited state share similar geometry Strong vibronic coupling is responsible for the b2 and b1 fundamentals Computational modeling of the electronic spectroscopy in progress Dispersed fluorescence on more peaks in the excitation spectrum Photochemically react cyanoacetylene and benzene

Acknowledgments Professor Timothy Zwier Zwier Group Professor Lyudmila Slipchenko Claudia Viquez Rojas

Experimental: Resonant Two-photon Ionization (R2PI) Supersonic Expansion Sample heated to 60°C Ion Chamber Laser Ports 2 Stage Ion Acceleration Einzel Lens Pulsed Valve MCP Time-of-Flight Tube Mass Gate Pulser Vibrationally cooled to zero-point levels S0

Excited State Lifetime Bi-exponential decay pattern: Short-lived component ≤ 10 ns Long-lived component > 800 ns M+ + e ISC Excited state calculations using TD-DFT were performed with a ωB97X-D basis set at 6-31+G(d) level of theory.

Rotational Band Contour of 35,242cm-1 Calculations predict TDM of S1 from S0 along c-axis TDM of S2 from S0 along a-axis Dye-laser resolution of 0.06 cm-1 Experiment suggests it is not due to S0-S1

How are b1 fundamentals gaining intensity in emission? C2ν Cs A1xb1=B1 Optimized S1 geometry: In-plane deformation of C3N chain S6 B2 A’ A2 A1 b1 a1 b2 S1 S2 Vibronic coupling S0 S5 A1 A’ S4 B2 A’ S3 A2 A” S2 A1 A’ A2xb2=B1 S1 A2 A” b2 member of tunneling doublet can mix with b1 fundamentals in S2(A1) state Forbidden in C2v Oscillator strength S0-S2 0.2482 S0-S1 0.0021 S0 A1 A’

Molecular Orbitals Visualized (LUMO) (LUMO) (HOMO) S0-S1 S0-S2

Calculated Geometry changes

Pertinent Character Tables Cs