1. 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

2. 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

3. 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

4. Experimental: Laser-Induced Fluorescence
Laser Induced Fluorescence Chamber

5. LIF

6. 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

7. 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

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

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

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

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

12. 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

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

14. 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

15. 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.

16. 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

17. 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-S
S0-S S0 A1 A’

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

19. Calculated Geometry changes

20. Pertinent Character TablesCs