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The H 3 + + H 2 Reaction; A Possible Mechanism for para - H 3 + Enrichment in the Diffuse Interstellar Medium. Lieutenant Colonel Brian A. Tom, USAF University of Illinois at Urbana-Champaign Inaugural MWAM, 2008. H 3 + - Abundant and Reactive. (Science, 279 , 1910, 1998) .

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Slide1 l.jpg

The H3+ + H2 Reaction; A Possible Mechanism for para- H3+ Enrichment in the Diffuse Interstellar Medium

Lieutenant Colonel Brian A. Tom, USAF

University of Illinois at Urbana-Champaign

Inaugural MWAM, 2008


H 3 abundant and reactive l.jpg
H3+ - Abundant and Reactive

(Science, 279, 1910, 1998)

(ApJ, 183, L17-20, 1973)

(Nature, 384, 334, 1996)

(ApJ, 185, 505, 1973)

(Phys. Rev., 26, 44, 1925)


H 3 an astrophysical probe l.jpg
H3+ - An Astrophysical Probe

H2

H3+

Para

Para

Ortho

Ortho

(3:1)

(2:1)

T. Oka, PNAS, 103, 12235, (2006)


Para h 3 is enriched in diffuse clouds l.jpg
Para-H3+ is Enriched in Diffuse Clouds

  • Texcitation measured

  • from H3+ is consistently

  • ~ 40 K lower than H2 –

  • derived Trot ~ 70 K

  • This indicates para-H3+

  • is enriched to ~ 65%

para-H3+

ortho-H3+

Indrioloet al., Ap. J., 671, 1736, (2007)

The cause?

Reaction-induced spin modification

H3+ + H2H2 + H3+



H 3 h 2 h 2 h 3 l.jpg
H3+ + H2H2 + H3+

Identity

+

+

+

+

+

+

Hop

Exchange

M. Cordonnier et al., J. Chem. Phys., 113, 3181, (2000)


H 3 h 2 h 2 h 37 l.jpg

para-H3+ + ortho-H2→ortho-H3+ para-H3+

Hop 2/3 1/3

Exchange 1/3 2/3

para-H3+ + para-H2 → ortho-H3+ para-H3+

Hop 0 1

Exchange 1/3 2/3

H3+ + H2H2 + H3+

ortho-H3+ + ortho-H2

ortho-H2 + ortho-H3+

ortho-H3+ + para-H2

ortho-H2 + para-H3+

para-H3+ + ortho-H2

para-H2 + ortho-H3+

para-H3+ + para-H2

para-H2 + para-H3+

T. Oka, J. Mol. Spec., 228, 635, (2004)


H 3 h 2 h 2 h 38 l.jpg
H3+ + H2H2 + H3+

Problem

ortho-H2

  • Previous model does

  • not account for energy

  • differences between

  • ortho and para ground

  • states

120 cm-1

para-H2

  • Park and Light have

  • addressed this

K. Park and J. Light, J. Chem. Phys., 126, 044305, (2007)



Spectroscopy l.jpg

R(1,0)

R(1,1)u

500

E(cm-1)

J

3

315 cm-1

2

237 cm-1

169 cm-1

87 cm-1

1

64 cm-1

0

0

K

0

1

2

3

(ortho) (para) (para) (ortho)

Spectroscopy

  • Temperature

  • Para-H3+ fraction


Spectroscopy11 l.jpg
Spectroscopy

Pulsed Source

Para-H2

generator

Telescope

InSb

LiNbO3

Achromat

Glan Prism

Nd:YAG

AOM

λ/4

λ/2

Wavemeter

Ti:Sapphire

λ/2



Temperature and para fraction l.jpg
Temperature and Para Fraction


An explanation for enrichment l.jpg
An Explanation for Enrichment?

0.79 ± 0.11

  • Using  = 0.51 ± 0.11, and  = 0.79 ± 0.11;

  • The average para-H3+ fraction measured from 9 diffuse cloud sightlines is 0.65 ± 0.15

Y. Shefferet al., accepted for Astrophys. J. (2008)


Conclusions l.jpg
Conclusions

  • H3+ plays an important role in the interstellar medium

  • We have inferred  = kH/kE = 0.79 ± 0.11 for

    60-100 K

    • Could explain para-H3+ enrichment in diffuse ISM

    • More experiments are necessary to understand the underlying process

  • Texcitation by itself is not a reliable measure of rotational temperature in the ISM


Slide16 l.jpg

Acknowledgments

  • Andrew Mills, Kyle Crabtree, Michael Wiczer

  • McCall Group



Motivation l.jpg
Motivation

H2+ + H2 → H3+ + H

He

Cosmic Rays

H2+

H+ and H2+

H

H3+

H+

O, C, N, Ne, Mg, Si, Fe…

T. R. Hogness and E. G. Lunn, Phys. Rev., 26, 44, (1925)

T. Oka, PNAS, 103, 12235, (2006)