Methyl Torsional Levels in 9-Methylanthracene

Masaaki Baba (Kyoto Univ. Japan)

Yuki Noma (Kyoto Univ. Japan) Shunji Kasahara (Kobe Univ. Japan)

Takaya Yamanaka (IMS, Japan)

Jon T. Hougen (NIST, Gaithersburg)26930 26931 26932 26933

26930.5 26930.6 26930.7 26930.8 26930.9 26931

cm-1

cm-1

dissociation

ISC

T1

fluo.

S0

phos.

IC

S1

abs.

IVR

S2

Vibronic Coupling (NBO)

Spin-orbitCoupling

Coriolis Coupling

Excited-state Dynamics

CH3 Internal Rotation (Torsion)

• How large is the barrier height V3 and V6 ?

• Enhancement of radiationless transitions.

¶ Density Increment of coupling levels

¶ Vibrational mixing including out-of-plane modes

n

n nVV )cos1(2

1)(

CH3 Torsion of Toluene

Staggered Eclipsed

V3 = 0

V6(S0) = -4.874 cm-1

V6(S1) = -26.376 cm-1

D. R. Borst and D. W. Pratt, J. Chem. Phys. 113, 3658 (2000)

y(a)

z(b)x(c)

μ

Molecular Symmetry Group G12 　 (C3v×C2)

G12 　 is isomorphic to the D3h group.

0 100 200 300 400

0

100

200

300

V6 (cm-1)

Level Energy (cm-1)

6a1’

3a2”

3a1”

6a2’

0a1’

2e’1e”

4e’

5e”

7e”

Energy Levels of CH3 Torsion of Toluene or 9MA

.0

,2,1,0

6

2

Vwhen

m

FmE

2800028500

2700027500

CH3

Fluorescence Excitation Spectra in Supersonic Jets

000

000

cm-1

CH3

ψ50

ψ53

ψ47

HOMO

ψ48

LUMO

ψ49

ψ46

ψ52

LUMO

ψ51

HOMO

Molecular Orbitals and S1 - S0 Transition

Fluorescence Excitation Spectrum of 9MA

1. J. A. Syage, P. M. Felker, and A. H. Zewail, J. Chem. Phys. 82, 2896 (1985)

2. F. Tanaka, S. Hirayama, and K. Shobatatake, Bull. Chem. Soc. Jpn. 59, 2011 (1986)

3. Y. Stepanenko, A. L. Sobolewski, and A. Mordzinski, J. Mol.Spectrosc. 233, 15 (2005)

4. M. Nakagaki, E. Nishi, K. Sakota, H. Nakano,and H. Sekiya, Chem. Phys. In press.

27000275002800028500cm-1

Rotational envelopes

269252693026935cm-1

273102731527320cm-1

26985269902699527000cm-1

0a1’→ 3a1”0a1’→ 0a1’1e”→ 1e”

1e’→ 4e’

Assignments can be confirmed by OODR.

Fluorescence Excitation Spectrum of 9MA in a Supersonic Jet

Energy Levels of CH3 Torsion of 9MA

0 100 200 300 400

0

100

200

300

V6 (cm-1)

Level Energy (cm-1

)

6a1’

3a2”

3a1”

6a2’

0a1’

2e’1e”

4e’

5e”

7e”

40 cm-1

S1

105 cm-1

S0

0a1’→ 0a1’ 1e”→ 1e”← 0.8 cm-1 →

Energy Levels of CH3 Torsion of 9MA4e'3a1"

3a2"2e'1e"0a1' 0 cm-1

520

57

23

72S1

V6 = 40 cm-1

F = 5.2 cm-1

S0

4e'

3a1"

3a2"2e'1e"0a1'V6 = 105 cm-1 0 cm-1

41626

79

110

F = 5.2 cm-1

0 cm-14.3

1625

79

100

0 cm-15.1

2038

57

85

Calc.

Calc.

Barrier Height to CH3 Rotation (cm-1)

S0 -4.874 81 25

S1 -26.376 25 (V3) 10 (V6)

Barrier Height to CH3 Rotation (cm-1)

S0 ~105 73 ~0

S1 ~40 292 ~0

Single Vibronic Level Dispersed Fluorescence Spectrum of 9MA in a Supersonic Jet

IVR starts

at 388 cm-1.

Enhancement of IVR by CH3

J. B. Hopkins, D. E. Powers, and R. E. Smalley, J. Chem. Phys. 71, 3886 (1979)

IVR in Anthracene

W. R. Lambert, P. M. Felker, and A. H. Zewail, J. Chem. Phys. 81, 2209 (1984)

H. Ishikawa, Ph.D. Thesis, Kyoto Univ. 1993.

Rotational Structure of Vibronic Bands of Toluene

CH3 Torsion of Toluene

D. R. Borst and D. W. Pratt, J. Chem. Phys. 113, 3658 (2000)

UV

CW YVO4 LaserTi:Sapphire Ring Laser

PMT

PhotonCounter

Magnet

ΔE < 0.0001 cm-1

Computer

Millenia X CR899-29

Wavetrain

Pulse nozzle

Collimated Molecular Beam and Single-mode Laser

CH3

Ultrahigh-Resolution Spectrum of 0-0 Band

26930 26931 26932 26933

26930.5 26930.6 26930.7 26930.8 26930.9 26931

cm-1

cm-1

1e’’→1e’’

0a1’→ 0a1’

-3 -2 -1 0 1 2 3

-3 -2 -1 0 1 2 3

-3 -2 -1 0 1 2 3

Calculated Spectra of 9MAA-type

B-type

C-type

cm-1

26930 26932

9MAcalculation

experiment

cm-1

Rotation-torsion Hamiltonian

zFyxzF pPACPBPPA

VFpH

'2

)6cos1(2

1ˆ

222

62

yxzF

z

ICIBIIA

IIIF

2/,2/),(2/

/12/222

2

22

2)1(

2

|ˆ|

622 VFmmKAK

CBAJJ

CB

JKMmHJKMm

FF

0 0.1 0.2 0.3

H = 0T

H = 1.2T

9MA 0-0 Band

cm-1

Relative wavenumber

Ultrahigh-resolution Spectrum and Zeeman Effect

• The potential barrier to rotation (V6) is estimated to be 110 (S0)and 40 (S1) cm-1, which is higher than that in toluene.

• The transition energy of 1e”→ 1e” is larger than 0a1’→ 0a1’ by 0.8 cm-1.

• IVR take places at the vibronic levels higher than 388 cm-1.

• The interaction with the triplet state is weak.

CH3 Levels of 9MA and the Excited-state Dynamics