Rotational and Vibrational Energy Transfer from the First Overtone Stretch of Acetylene

Keith FreelJiande Han

Michael C. Heaven

Purpose:Optically Pumped Molecular Gas Lasers

3100 3120 3140 3160 31800

1

2

3

4

5

Am

plitu

de (a

rb. u

nits

)

Wavelength (nm)

R ~90% @ 3 μm

80 cm

2 m

CaF 2

window

detector/spectrometer

R~ 90%@ 3 μm

C2H2, 2 Torrns OPO

R (7)

00000

10100

(01002100000003201020 )

3 μm

A.V.V. Nampoothiri, A Ratanavis, N. Campbell, and W. Rudolph. Optics Express, 18(3), 2010, p1946.

Purpose:Optically Pumped Molecular Gas Lasers

3100 3120 3140 3160 31800

1

2

3

4

5

Am

plitu

de (a

rb. u

nits

)

Wavelength (nm)

R ~90% @ 3 μm

80 cm

2 m

CaF 2

window

detector/spectrometer

R~ 90%@ 3 μm

C2H2, 2 Torrns OPO

R (7)

00000

10100

(01002100000003201020 )

3 μm

A.V.V. Nampoothiri, A Ratanavis, N. Campbell, and W. Rudolph. Optics Express, 18(3), 2010, p1946.

1) Total removal from 10100 rotational levels

2) Rotational Energy Transfer

3) Vibrational Energy Transfer

• To what states?• How fast?

IR-UV-DR (Time Resolved) Spectroscopy

Three types of experiments1. UV scan2. IR scan3. Time delay scan

(00000)00 X S+g

(10100)00

Direct Excitation: (V”, J”, K”) (V,J,K) V’, J’, K’Indirect Transfer: (V”, J”, K”) (V,J,K)init (V,J,K)final (V’,J’,K’)

A 1Au (v3’ + v5’)

LIF

(v1v2v3v4v5)l> 5 ns

Spectroscopy of Acetylene

n”1

n”2

n”3

n”4

n”5

S+g

S+g

S+u

Pg

Pu

Ground State X S+g (D∞h) First Excited State A 1Au (C2h)

n'1 CH sym str

n'2 CC stretch

n'3 trans bend

n’4 torsion

n'5 CH anti str

n‘6 cis bend

ag

ag

ag

au

bu

bu

3372.85 cm-1

Watson. J Molec. Spec. 95, 1982, 101. Merer. Mol. Phys. 101(4-5), 2003, 663.

1974.32 cm-1

3288.39 cm-1

612.87 cm-1

730.33 cm-1

2880.5 cm-1

768.26 cm-1

2857.41 cm-1

764.91 cm-1

1047.55 cm-1

1386.9 cm-1

Tobiason. J. Chem. Phys. 99(2), 1993, 928.Herman et al. J. Phys. Chem. Ref. Data, Vol. 32, No. 3, 2003. Also MF07.

Experimental Setup

LIF Flow CellPM

TExcimer pumped Dye Laser with Doubling Crystal

Nd:Yag pumped OPO/OPA

Computer

Boxcar with Preamp

Optics/Filters

Pump1.5 mm

Probe250 nm

Delay Generator

~ 0.1 Torr C2H2

1. UV Scan – 20 ns delay

(00000)00X S+g

(10100)00

A 1Au (v3’ + v5’)

J=4

J=14J=12J=10J=8J=6

nm (Simulation - PGopher)

P R

Q(6) Q(10)Q(14)

R-branch

P(7)P(11)P(9)

J=4

J=14J=12J=10J=8J=6

nm (Simulation - PGopher)

P R

Q(6) Q(10)Q(14)

R-branch

P(6)P(10)P(8)

1. UV Scan – 220 ns delay

(00000)00X S+g

(10100)00

A 1Au (v3’ + v5’)

Density Of States

cm-1 cm-1

Vibrational Rotational

0.3 states/cm-1 > 6 states/cm-1

Herman et al. J. Phys. Chem. Ref. Data, Vol. 32, No. 3, 2003.

10100

Vibrational Energy Transfer

nm (UV Scan)

(00000)00 X S+g

(10100)

A 1Au (v1’ + v3’)

a = c1|00200> - c2|11020>b = c2|00200> + c1|11020>

A-Xb A-Xa

Band heads

Obs. (Odd DJ)Pumped J=8

Calc. PGopher

10100 Xa + 41 cm-1

10100 Xb + 53 cm-1

Herman et al. J. Phys. Chem. Ref. Data, Vol. 32, No. 3, 2003. Merer. Mol. Phys. 101(4-5), 2003, 663.

g

u

g

g

2. IR Scan Experiment

1505 1510 1515 1520 1525 1530 1535IR wavelength (nm)

120 ns 220 ns

(00000)00 X S+g

(10100)00

A 1Au (v3’ + v5’)

IR Scan

UV Fixed

R(13)P(15)

3. Time ScanTotal Removal From 10100 (J=2 – J=16)

ns

J Ki/10-10

(cm3 s-1)+/- 0.3

Crim

2 7.6 NA

4 7.9 NA

6 6.5 NA

8 8.4 8.2

10 8.6 8.5

12 8.8 9.0

14 8.8 10.9

16 8.7 8.8

I(t) = A exp (-Kint)

J. D. Tobiason, Ph.D. thesis, University of Wisconsin-Madison, 1992.

RET kinetics – measuring kif

J kiJ=14/10-10 (cm3

s-1)+/- 0.3

14 8.6 (Total Removal)

2 0.7

4 1.0

6 1.3

8 1.3

10 1.4

12 1.7

16 1.3

18 0.9

20 0.5

Nf(t)/No = If (t) = (kif /Ki)[1-exp(-Kint)] Ki = total removal rate from ikif = state to state removal rate from i to f

0 100 200 (ns)

0 400 800 1200 1600 2000 2400 2800 3200

20 and 220 ns UV Scans with Simulation for assignmentBackground Considerations

Q(16)

Q(12)Q(8)

Q(20)

20 and 220 ns UV Scans with Simulation for assignmentBackground Considerations

Q(16)

Q(12)Q(8)

Q(20)

Payne. Z. Phys. Chem. 219, (2005) 601–633Payne. J. Phys. Chem. A, Vol. 110(9), (2006) 3307

Conclusions

• IR-UV DR spectroscopy has been used to identify VET and RET

• Total removal rates were measured from the 10100 state and match previous measurements.

• VET to the 00200/11020 diad was observed.• Measured State-to-State RET rates are too

large due to complex ET pathways.

Thank You For Listening

• Advisor: Michael Heaven• Postdoc Fellow: Jiande Han• Group Members: Ivan Antinov, Beau Barker,

Md. Humayun Kabir