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


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


4

Other experimental workOther experimental work

hop

:exch

ang

e

temperature

Experimental data

hop

exch

increases withincreasing T


5

Experimental setupExperimental setup


6

Hollow cathode cellHollow cathode cell


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)


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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)


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


10

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

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


11

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

Tkin = 135 K


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


13

H3+ + H2 H2 + H3

+H3+ + H2 H2 + H3

+

“identity”

“hop”

H5+

“exchange”

3

1111

6


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


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

Spectroscopic measurements of the reaction H 3 + + H 2 H 2 + H 3 +

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