1. Spectroscopy of 4-Isocyanobenzonitrile (4IBN)
Joseph A. Korn, Deepali N. Mehta-Hurt, and Timothy S. Zwier
68th International Symposium on Molecular Spectroscopy
TK10
Department of Chemistry, Purdue University
West Lafayette, IN 47905

2. Titan’s Atmosphere Cassini-Huygens
N2, Trace hydrocarbons
Formation of polymeric “Tholins”
Model of Prebiotic Earth?
160 chemical species detected astronomically
Many contain C and N
CN functionality
1. Waite Jr., J.H.; et al. ,Science, , 2.

3. Isonitriles Two resonance Structures Avenue for nitrile transport
Interesting Chemistry
Nitrile/isonitrile photoisomerization
Hydrolysis to formamides
Ea=124 kJ/mol
When R=H
1. E. Hébrard et al; Astronomy & Astrophysics;
2. Nenajdenko, V., Isocyanide Chemistry. Wiley-VCH:Weinheim, 2012

4. Dicyanobenzene and Diisocyanobenzene
D2h
No permanent dipole
C2v
Permanent dipole
μ = Debye

5. Dicyanobenzene and Diisocyanobenzene
35566 cm-1
000 ?
1. Fujita et al., J. Phys Chem , ,
2. Data acquired by Deepali Mehta-Hurt. Unpublished.

6. Experimental Supersonic Expansion
Boltzmann Distibution
Pre-expansion
Supersonic Expansion
Cools to zero-point vibrational level.
High pressure backing gas (He: 40 psi)
Expanded into vacuum through a pinhole
Collisional Cooling to zero point vibrational level

7. Resonant Two-Photon Ionization (R2PI)
Ionization Continuum S0 Sn
Tuned Laser
Ionization Laser (193 nm)

8. Dispersed FluorescenceSn
Fluorescence Dispersed

9. R2PI of 4-IBN
Assignments made with assistance of dispersed fluorescence and ab initio calculations.

10. Dispersed Fluorescence of 4-IBN
Intensity from Δv=0 Franck-Condon factors in 33, 34, and 11
Duschinsky mixing causes change on Mulliken mode label for 22

11. Duschinsky Mixing in 4IBN
Ground
Excited
20
20
21
21

12. Franck-Condon Factors in 4IBN
Δv=+1
Δv=0
Δv=-1
Δv=+1
Δv=0
Δv=-1
In emission:
ΔV=-1
ΔV=+1
ΔV=0
Δv=0 Franck-Condon factors give intensity to some modes in 4IBN
exc

13. Comparison to Ground State Calculations
Mulliken
(Varsanyi)
4IBN
Experimental
Calculated
13(6a)
384
386 34
466
479 33
544
557
12(19a)
652
662 11
817
828
9(8a)
1208
1201
Reasonable agreement
Possibility of Duschinsky Mixing resulting in cross sequence bands
Calculations at B3LYP/6-31G+(d)

14. R2PI of 4-IBN Explained Modes 33 and 34 have b2 symmetry
State
Sym. f S0 A1 - S1 B2
.0102 S2
.5067
Modes 33 and 34 have b2 symmetry
B2 x b2 =A1 :: Herzberg-Teller coupling
Most other modes are A1
In-plane fundamentals

15. Comparison to Excited State Calculations
Reasonable agreement
Out of plane vibrational intensity likely due to coupling with high oscillator strength of S2
Mulliken
(Varsanyi)
Frequency (Rel. cm-1)
Experimental
Calculated
000
(0)
3410
510
506
3310(6b)
447
2010
429*
433
2210(16b)
322
282
1110
758
770
910(8a)
1177
1192
710(12)
1268
1241
Calculations at B3LYP/6-31G+(d)
*Based on 2020 = 858 cm-1

16. Dicyanobenzene, Diisocyanobenzene, and 4IBN

17. Summary 4IBN has been investigated by R2PI and dispersed fluorescence.
There appears to be Herzberg-Teller coupling to a strong S2.
Origin (35543 cm-1) lies between that of the dicyanobenzene and diisocyanobenzene.
The Spectrum of 4IBN is a hybrid of the two other species

18. Future Work
Further assignment of vibronic bands
Spectroscopy of S2

19. Acknowledgements Dr. Timothy S. Zwier Zwier Lab: Funding:
Dr. Vanesa Vaquero –Vara
Dr. Ryoji Kusaka
Evan Buchanan
James Redwine
Zachary Davis
Deepali Mehta-Hurt
Nathanael Kidwell
Jacob Dean
Di Zhang
Patrick Walsh
Joseph Gord
Nicole Burke
Alex Parobek
Polina Navotnaya
Rachel Clayton
Funding:
(NASA, not Elmo)