Vibronic Spectroscopy of Jet-Cooled 1,4-Phenylene Diisocyanide

6/21/11 1

DEEPALI N. MEHTA, ANNA K. GUTBERLET, AND TIMOTHY S. ZWIER

66th International Symposium on Molecular SpectroscopyTG07

Department of Chemistry, Purdue UniversityWest Lafayette, IN 47907

Motivation

2

[1] Kemsley, J. ,Chemical and Engineering News, 2007, 85, 11[2] Raulin, F., Space Sci. Rev. 135, 2008, 37-48

Figure 11: Schematic of reactions in Titan’s atmosphere.

• Titan is a model system for studies of primordial Earth2

• Titan’s chemistry occurs via ion and neutral pathways. 2

• 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 24: Density as a function of mass, for compounds present in Titan’s atmosphere. Note the presence of mass 128.

128 amu

Motivation

4

• Species such as HCN, HC3N, C2N2, and NH3 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 CNN

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

N NC C

C CN N

C CHC CH

Experimental

6

Collisional cooling to zero-point vibrational levels

Sample entrained in high pressure backing gas

Supersonic Expansion

S0

Cooling

Laser Induced Fluorescence

UV

lase

r (tu

ned)

(S0,v=0)

A*(Sn)Detect total

fluorescence

PMT

UV

lase

r (fix

ed)

Total

fluorescence

CCD

Dispersed Fluorescence

Experimental

7

LaserPorts

2 Stage IonAcceleration

Einzel Lens

Pulsed Valve

MCP

Time-of-Flight Tube

Mass Gate Pulser

1C-R2PI

Ionization continuum

Sn

S0

2C-R2PI

Sn

S0

Resonant 2 Photon Ionization (R2PI)

Tuned Laser

Fixed Laser

Tuned Laser

Experimental

8

UV-UV Holeburning

S0

Sn

20 Hz Probe(Tuned)

10 HzHB

Δt = 200 ns

Ionization continuum

Δt = 50-200 ns

HoleburnLaser (10Hz)

ProbeLaser (20Hz)

Spectra collected using active baseline subtraction

Wavenumbers (cm-1)

Probe only

Difference

*

Probe + Holeburn

Lasers spatially overlapped but temporally separated

2.5

2.0

1.5

1.0

0.5

0.0

Inte

nsi

ty

4000039000380003700036000Wavenumbers (cm

-1)

35,566

36,024(rel=458)

*

*

*

*

LIF Spectrum of 1,4-Phenylene Diisocyanide (PDI)

9

Origin at 35,566cm-1

S0-S1 LIF excitation spectrum, spanning 35,000-40,500cm-1. The S0-S1 electronic origin of 1,4-PDI has been identified as 35,566cm-1. Peaks marked * were anticipated to be due to other species.

Hole-burning Spectra

10

Inte

nsity

(A

rbitr

ary

Uni

ts)

3640036200360003580035600

Wavenumbers (cm-1

)

R2PI

Hole-burning

Vibronic transitions due to same ground state

000

*

Dispersed Fluorescence of S0-S1 Origin Band

11

Inte

nsity

-2500 -2000 -1500 -1000 -500 0Relative Wavenumbers / (cm

-1)

701

393 (ag)17

01

501 (b3g)

1601

650 (b3g)

1501

1327 (b3g)

1475

301

1671 (ag)

1708

1858

Dispersed fluorescence of S0-S1 electronic origin at 35,566cm-1.

-3000 -2000 -1000 0Relative Wavenumbers (cm

-1)

Dispersed fluorescence of vibronically coupled mode 17 at 36,024cm-1. Inset within the graph is a visualization of normal mode 17, which has b3g symmetry.

ν17

1711

Δv=0171

0

Δv=-1171

2

Δv=+1

Dispersed Fluorescence of +458cm-1 Band

12

Vibronic Coupling and Tentative Assignments

13

Table 2. Experimental Calculated Symmetryν3 1671 1679 ag

ν5 1204 1215 ag

ν6 823 842 ag

ν7 393 396 ag

ν11 403 414 b2g

ν12 187 182 b2g

ν15 1327 1347 b3g

ν16 649 662 b3g

ν17 500 508 b3g

ν35 305 303 b3u

ν36 83 84 b3u

Calculated frequencies provided as courtesy of Head-Gordon group, using Qchem with rimp2-cc-pvdz .

Table 1. Symmetry Oscillator Strength

S1 B2u 0.0015

S2 B1u 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

B2u × b3g=B1u

2.5

2.0

1.5

1.0

0.5

0.0

Inte

nsi

ty

4000039000380003700036000Wavenumbers (cm

-1)

35,566

36,024(rel=458)

*

*

*

*

LIF Spectrum of 1,4-Phenylene Diisocyanide (PDI)

14

Origin at 35,566cm-1

S0-S1 LIF excitation spectrum, spanning 35,000-40,500cm-1. The S0-S1 electronic origin of 1,4-PDI has been identified as 35,566cm-1.

1710

000

Identification of S0-S2

15

S0-S2 LIF excitation spectrum, spanning 40,500-44,100cm-1, approximately 6,100cm-1 above the S0-S1 origin.

Inte

nsity

(A

rbitr

ary

Uni

ts)

42400422004200041800

Wavenumbers (cm-1

)

R2PI

LIF

S0-S2 origin

1000

800

600

400

200

0

Inte

nsi

ty

-12,000 -10,000 -8,000 -6,000 -4,000 -2,000 0Relative Wavenumbers (cm

-1)

Dispersed Fluorescence from S2

16

Dispersed fluorescence of S0-S2 at 41,711 cm-1. The broadened emission near the S0-S1 origin suggests a S2S1 internal conversion, followed by fluorescence to the ground state.

S0

S1

S2

Internal Conversion

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.

366003640036200360003580035600Wavenumbers (cm

-1)

1,4-Phenylene Diisocyanide35,566cm-1

466cm-1

N NC C

C CN N

C CHC CH

18

Monosubstituted Benzene Origin (cm-1) Relative Absorption (cm-1)ethynylbenzene8 35879 0phenyl cyanide8 36516 637phenyl isocyanide8 36706 827

Disubstituted Benzene (para) Origin (cm-1) Relative Absorption (cm-1)para-diethynylbenzene6 34255 0para-dicyanobenzene7 35120 8651,4-PDI (para-diisocyanobenzene) 35566 1311

Summary

• A fluorescence excitation spectrum spanning the range 35,500-44,100 cm-1 (226.5-281.5 nm) has been recorded.

• The S0-S1 origin was identified at 35,566cm-1, and the S0-S2 origin was identified nearly 6,100 cm-1 above.

• Modes with b3g symmetry exhibit strong vibronic coupling to nearby B1u second excited state (S2).

[8] A. R. Muirhead, A. Hartford, Jr, K-T Hurang, J. R. Lombardi, J. Chem. Phys., 1972, 56, 4385-4393

Future Directions

19

• SpectroscopyPhotoionization efficiency scansMore complete analysis of vibronic structure in S1 manifold

• Photochemical studiesLong-lived excited states as in phenylacetylene?Study NC to CN isomerization

Acknowledgements

20

Professor Timothy S. ZwierThe Zwier Group

Josh Sebree (TB08, TD11)Evan Buchanan (WI10)

Zachary DavisJames Redwine

Jacob Dean (RG11)Nathanael Kidwell (WI11)

Joseph KornDi Zhang