spectroscopic measurements of the reaction h 3 + + h 2 h 2 + h 3 +

Spectroscopic measurements of the reaction H3

+ + H2 H2 + H3+

Spectroscopic measurements of the reaction H3

+ + H2 H2 + H3+

Kyle N. Crabtree, Carrie A. Kauffman, Brian A. Tom, Eftalda Becka, Brett A. McGuire, Benjamin

J. McCall

University of Illinois

Kyle N. Crabtree, Carrie A. Kauffman, Brian A. Tom, Eftalda Becka, Brett A. McGuire, Benjamin

J. McCall

University of Illinois

20 June 2011 66th OSU International Symposium on Molecular Spectroscopy

2

H3+ + H2 H2 + H3

+H3+ + H2 H2 + H3

+

“identity”

“hop”

H5+

“exchange”

3

1111

6

para-H3+ ortho-H3

+

1/2 3/2

H3+ + H2 reaction important for

thermalization of H3+ in interstellar

clouds(see TF09, 160 MA, 3:52 pm)

= kH/kE

20 June 2011 66th OSU International Symposium on Molecular Spectroscopy

3

Previous experimental workPrevious experimental work

M. Cordonnier et al., J. Chem. Phys. (2000), 113, 3181-3193.M. Cordonnier et al., J. Chem. Phys. (2000), 113, 3181-3193. = 2.4 + 0.6 @ 400 K

20 June 2011 66th OSU International Symposium on Molecular Spectroscopy

4

Other experimental workOther experimental work

hop

:exch

ang

e

temperature

Experimental data

hop

exch

increases withincreasing T

20 June 2011 66th OSU International Symposium on Molecular Spectroscopy

5

Experimental setupExperimental setup

20 June 2011 66th OSU International Symposium on Molecular Spectroscopy

6

Hollow cathode cellHollow cathode cell

20 June 2011 66th OSU International Symposium on Molecular Spectroscopy

7

R(1,0)2725.9 cm-1

R(3,0)2930.1 cm-1

R(3,3)l

2829.9 cm-1

R(1,1)u

2726.2 cm-1

R(2,1)u

2826.1 cm-1

R(3,1)u

2928.3 cm-1

R(2,2)l

2762.1 cm-1

R(3,2)u

2923.3 cm-1

Target transitionsTarget transitions

Kinetic and rotational temperature

p-H3+ fraction (p3)

20 June 2011 66th OSU International Symposium on Molecular Spectroscopy

8

H3+ pressure dependenceH3+ pressure dependence

• Decrease in H3+ number density with increasing pressure

• 3-body collisions (H3+ + 2H2 H5

+ + H2)

• To measure hop:exchange ratio of the bimolecular H3+ +

H2 reaction, measure p3 as a function of p2 at two pressures for each temperature

• Decrease in H3+ number density with increasing pressure

• 3-body collisions (H3+ + 2H2 H5

+ + H2)

• To measure hop:exchange ratio of the bimolecular H3+ +

H2 reaction, measure p3 as a function of p2 at two pressures for each temperature

Uncooled cell (350 K) Liquid N2 cooled cell (135 K)

20 June 2011 66th OSU International Symposium on Molecular Spectroscopy

9

H3+/H2 para fraction relationshipsH3+/H2 para fraction relationships

Uncooled cell (350 K) Liquid N2 cooled cell (135 K)

2-body HT 3-body HT Low temperature

20 June 2011 66th OSU International Symposium on Molecular Spectroscopy

10

Uncooled plasma (350 K) fitUncooled plasma (350 K) fit

No evidence for influence of nuclear-spin-dependent 3-body collisions in data

20 June 2011 66th OSU International Symposium on Molecular Spectroscopy

11

Liquid N2 cooled plasma (135 K) modelingLiquid N2 cooled plasma (135 K) modeling

Tkin = 135 K

20 June 2011 66th OSU International Symposium on Molecular Spectroscopy

12

Summary of experimental dataSummary of experimental data

= 2.2 + 0.3T = 450 K

decreases with temperature: 1.6 at 350 K down to 0.5 at 135 K

20 June 2011 66th OSU International Symposium on Molecular Spectroscopy

13

H3+ + H2 H2 + H3

+H3+ + H2 H2 + H3

+

“identity”

“hop”

H5+

“exchange”

3

1111

6

20 June 2011 66th OSU International Symposium on Molecular Spectroscopy

14

Dynamics of ReactionDynamics of Reaction

C2v

D2dC2v

hop

exchange

At low temperatures, “statistical” hop/exchange =

0.5 seems valid

300

0 c

m-1

50 cm-11500 cm-1

PES: Z. Xie, B. J. Braams, & J. M. Bowman,J. Chem. Phys. (2005) 122, 224307.

Hop is dynamically faster than exchange; short complex lifetime favors hop

20 June 2011 66th OSU International Symposium on Molecular Spectroscopy

15

AcknowledgementsAcknowledgements

Kisam ParkMore information:

Tomorrow, TF09, 160 MA

K. N. Crabtree, B. A. Tom, B. J. McCall, J. Chem. Phys. (2011) 134, 194310.

K. N. Crabtree et al., J. Chem. Phys. (2011) 134, 194311.

http://bjm.scs.illinois.edu