new laboratory and theoretical studies of astrophysically important reactions of h 3 +

New Laboratory and Theoretical New Laboratory and Theoretical Studies of Astrophysically Studies of Astrophysically Important Reactions of HImportant Reactions of H33

++

Ben McCallBen McCall

Dept. of Chemistry Dept. of Astronomy

OutlineOutline

• Background– Importance of H3

+

– Interstellar Clouds• H3

+ in Diffuse Clouds– Abundance: H3

+ + e- → H + H + H– Ortho/Para: p-H3

+ + e- → H + H + H H3

+ + H2 → H3+ + H2

• H3+ in Dense Clouds

– Abundance: H3+ + O → OH+ + H2

– Puzzle: H3+ + O2 ↔ HO2

+ + H2

Astronomer's Periodic TableAstronomer's Periodic Table

H He

C N O Ne

Mg

Fe

Si S Ar

HH33++: Cornerstone of Interstellar Chemistry: Cornerstone of Interstellar Chemistry

H 2

H 2+

C H 3+

C H 5+

C H 4

C H2 3+

C H2 2

C H3+

C H3 3+

C Hm n

C H +

C H 2+

N H2+

H C O+O H +

H O2+

H O3+

H O2

O H

C H C N H2 5+

C H C N H3+

C H N H3 2+

H C N2+

H C N

C H N H3 2

C H N H2

C H C N3

C H C N2 5

C H

C H C O3+

C H O H3 2+

C H C O2

C H O H3

H C OC H O H

C H O C H

2

2 5

3 3

C H2 5+

C H2 4

H C O2 3+

C O3

C H2

H C N3 3+

H C N3

H C N5

H C N7

H C N9

H C N11

C H3

C 4+

C H4+

C H4 2+

C H4 3+

C H4

C H3 2

cosm ic ray

H 2N 2

C OO

H 2

H 2

e

e

e

ee

e

e

N

N H 3

H C N

C H C N3

e

C OH O2

C H O H , e3

C

H 2

H 2

H 2

e

e

C H 3+

e

e eH C N

C+

e

C+

H 2

e eC

+

H 2H 2

e

C O

C

H

+

e

e

8

7

6

5

4

3

2

Pro

ton

Affin

ity (e

V)

N

O2

H2

ON2

CO2

CH4

OHCC2

H2O

H2COCH

NH2

SiNH3

CO

Pro

ton

Affi

nity

(eV

)

H3+ + O H2 + OH+

OH+ + H2 H + H2O+

H2O+ + H2 H + H3O+

H3O+ + e- H2O + H

Interstellar Cloud ClassificationInterstellar Cloud ClassificationDiffuse clouds:

• H ↔ H2

• C C+

• n(H2) ~ 101–103 cm-3

– [~10-15 Torr]• T ~ 50 K

PerseiPersei

Photo: Jose Fernandez Garcia

Snow & McCallARAA, 44, 367 (2006)

Dense molecular clouds:

• H H2

• C CO• n(H2) ~ 104–106 cm-3

• T ~ 20 K

PoundApJ 493, L113 (1998)

OutlineOutline


+




+ + e- → H + H + H H3

+ + H2 → H3+ + H2




+ + H2

Rate = ke [H3+] [e-]

[H2]

Diffuse Cloud HDiffuse Cloud H33++ Chemistry Chemistry

H2 H2+ + e-

H2 + H2+ H3

+ + H

cosmic ray

H3+ + e- H + H2 or 3H

Rate =

Formation

Destruction

[H3+]

=

ke[e-]

Steady State[H2] =

(310-17 s-1)

(510-7 cm3 s-1) (2400) = 10-7 cm-3

L ~ 3 pc ~ 1019 cm

N(H3+) ≡ L × [H3

+] ~ 1012 cm-2

dense cloud value

ΔI/I ~ 0.01%

Lots of HLots of H33++ in Diffuse Clouds! in Diffuse Clouds!

8

6

4

2

0

H3+ C

olum

n D

ensi

ty (1

014cm

-2)

6543210

E(B-V) (mag)

OphP Cygni

HD 183143

WR 118

Cyg OB2 12

WR 104

Cyg OB2 5

WR 121

HD 168607

HD 194279

GC IRS 3

2 Ori

HD 20041

1.01

1.00

0.99

0.98

0.97

Rel

ativ

e In

tens

ity

3.7173.7163.7153.6693.6683.667Wavelength (µm)

R(1,1)u

R(1,1)l

R(1,0)

HD 183143

McCall, et al.ApJ 567, 391 (2002)

Cygnus OB2 12

N(H3+) ~ 1014 cm-2 ?!?

Big Problem with the Chemistry!Big Problem with the Chemistry!

Steady State: [H3+]

= ke [e-]

[H2]

To increase the value of [H3+], we need:

• Smaller electron fraction [e-]/[H2]

• Smaller recombination rate constant ke

• Higher ionization rate

(order of magnitude)

^

ruled out byobservations

Enigma of HEnigma of H33++ Recombination Recombination

• Laboratory values of ke have varied by 4 orders of magnitude!

• Problem: not measuring H3

+ in ground states

k e (c

m3 s

-1)

Larsson, McCall, & OrelChem. Phys. Lett., in press

Ion Storage Ring MeasurementsIon Storage Ring Measurements

20 ns 45 ns

electron beam

H3+

H, H2

+ Very simple experiment+ Complete vibrational relaxation

+ Control H3+ – e- impact energy

+ Rotationally cold ions from supersonic expansion source

CRYRING

30 kV30 kV

900 keV900 keV

12.1 MeV12.1 MeV

CRYRING ResultsCRYRING Results

• Considerable amount of structure (resonances) in the cross-section

• ke = 2.6 10-7 cm3 s-1

• Factor of two smallerMcCall et al.Nature 422, 500 (2003)

Agreement with Other WorkAgreement with Other Work• Reasonable agreement between:

– CRYRING• Supersonic expansion

– TSR• 22-pole trap

– Theory

S.F. dos Santos, V. Kokoouline, and C. H. Greene, J. Chem. Phys. 127 (2007) 124309

Big Problem with the Chemistry!Big Problem with the Chemistry!

Steady State: [H3+]

= ke [e-]

[H2]

To increase the value of [H3+], we need:

• Smaller electron fraction [e-]/[H2]

• Smaller recombination rate constant ke

• Higher ionization rate =7.410-16 s-1

(25× higher thandense clouds!)N. Indriolo, T. R. Geballe, T. Oka, &

B. J. McCall, ApJ 671, 1736 (2007)

Astrophysics!!

Low Energy Cosmic Rays?Low Energy Cosmic Rays?• Flux below <1 GeV essentially unconstrained

– magnetic field due to solar wind• Large low E flux can reproduce observations!

Photo: M.D. Stage, G. E. Allen, J. C. Houck, J. E. Davis, Nat. Phys. 2, 614 (2006)

1 MeV

2 MeV

10 MeV20 MeV

50 MeV(diffuse) (dense)

N. Indriolo, B. D. Fields & B. J. McCall, in preparation

OutlineOutline


+




+ + e- → H + H + H H3

+ + H2 → H3+ + H2




+ + H2

HH33++ Ortho/Para Ratio Ortho/Para Ratio

+

orthoI = 3/2

paraI = 1/2

+

Cygnus OB2 12

No

Np

go

gp

e-ΔE/kTex=

ΔE

R(1,0) R(1,1)

Tex ~ 27 Kbut

Tkin ~ 60 K

Why?

para-Hpara-H33++ + e + e-- vs. ortho-H vs. ortho-H33

++ + e + e--

Theory: S.F. dos Santos, V. Kokoouline, and C. H. Greene, J. Chem. Phys. 127, 124309 (2007)

normal H2

para H2

experiment

para-H3+

ortho-H3+

theory

Experiment: H. Kreckel, et al.Phys. Rev. Lett. 95, 263201 (2005)

TSR

K

para-H3+ fraction

unknown (~0.55?)

Recent CRYRING ResultsRecent CRYRING Results85% p-H3

+

[100% p-H3+]

50% p-H3+

[100% o-H3+]

×2!

B. Tom et al.,in preparation

• Big ortho-para difference

• But ortho/para H3+ may be

equilibrated by H3+ + H2 collisions

OutlineOutline


+




+ + e- → H + H + H H3

+ + H2 → H3+ + H2




+ + H2

HH33++ + H + H22 → (H→ (H55

++)* → H)* → H33++ + H + H22

“identity”

“hop”

“exchange”

H5+

1

3

6if purely statistical:α = hop/exchange = 0.5

Dynamical EffectsDynamical Effects

C2v

D2dC2v

“hop”

“exchange”

Not obvious that “statistical” α = hop/exchange = 0.5 is valid!

~300

0 cm

-1

~50 cm-1~1500 cm-1

Energetic EffectsEnergetic Effects• Angular momentum restrictions

– e.g. p-H3+ + p-H2

→ o-H3+ + p-H2

• At low T in pure p-H2, slow p-H3+ → o-H3

+

orthoI = 3/2

paraI = 1/2

paraI = 0

orthoI = 1

170 K

1/2 0 ↔ 3/2 0

Oka Group ExperimentsOka Group Experiments

o-H3+ p-H3

+

Pulsed Hollow CathodePositive Column Cell

Cordonnier et al. JCP 113, 3181 (2000)

p-H2

n-H2

o-H3+

p-H3+

n-H2 p-H2

hopexch ~2.4

T ~ 400 K

α = ≠ 0.5!

How does α vary with T?

Supersonic Expansion Ion SourceSupersonic Expansion Ion Source

• H3+ formed near nozzle

• [p-H2] / [H2] fixed– [H2] / [H3

+] >> Ncollisions

• [p-H3+] / [H3

+] reaches steady state in few coll.

• [p-H3+] / [H3

+] measured spectroscopically

H2Gas inlet

2 atm

Solenoid valve

-450 Vring

electrode

Pinhole flange/ground

electrode

H3+

McCall et al. PRA 70, 052716 (2004)

2.8 – 4.8 2.8 – 4.8 m DFG Systemm DFG System

Ti:Sapph700 – 990 nm

532 nmpump laser

reference cavity

dichroic

/2

Nd:YAG1064 nm

AOM

PPLN

25cm20cm

/2/4

Glanprism

20cmachromat

InSb mode-matching

lenses

ringdowncavity

Cavity Ringdown SpectraCavity Ringdown Spectra

• First results from our DFG laser!

• Clear enhancement of para-H3

+ in para-H2

• More enhanced in argon dilution

• Trot ~ 80 K– R(1,1)u vs R(2,2)l

ortho-H3+ para-H3

+

HH33++ + H + H22 Results Results

α=2.5α=1.0α=0.5

80 KPark & Light

JCP 126, 044305 (2007)

ζ Persei

Tex o/p H3+ ratio not

thermal, but steady state of H3

+ + H2

(Oka)

Tkin~60 K

OutlineOutline


+




+ + e- → H + H + H H3

+ + H2 → H3+ + H2




+ + H2

NO

Ne

HH33++ in Dense Clouds in Dense Clouds

CCO

8

7

6

5

4

3

2

Pro

ton

Affin

ity (e

V)

N

O2

H2

ON2

CO2

CH4

OHCC2

H2OCH

CO

Pro

ton

Affi

nity

(eV

)

H

NeHe

• Relatively few electrons• C → CO• H3

+ destroyed by proton transfer– CO– O, O2?

?

ζ [H2]

Dense Cloud HDense Cloud H33++ Chemistry Chemistry

H2 H2+ + e-

H2 + H2+ H3

+ + H

cosmic ray

H3+ + CO HCO+ + H2

Rate =

Formation

DestructionRate = kCO [H3

+] [CO]

ζ [H3

+] =kCO [CO]

Steady State

=(310-17 s-1)

(210-9 cm3 s-1)

[H2] (6700)

= 10-4 cm-3

(fast)

McCall, Geballe, Hinkle, & OkaApJ 522, 338 (1999) L ~ 1 pc ~ 3×1018

cm → N(H3+) ~ 3×1014 cm-2

H3+ + O OH+ + H2 Rate = kO [H3

+] [O]

210-9 cm3 s-1

0.810-9 cm3 s-1

=

??

HH33++ + O + O → OH→ OH++ + H + H22

Stephen Klippenstein (2008)

Ryan Bettens (1999)

• At T<50, kO kCO ζ or L ↑ by factor of ~2

Tcloud

OutlineOutline


+




+ + e- → H + H + H H3

+ + H2 → H3+ + H2




+ + H2

HH33++ + O + O22 ↔ HO↔ HO22

++ + H + H22

• HO2+ is last simple protonated species yet

to be observed spectroscopically• O2 difficult to observe in dense clouds;

HO2+ may be a useful tracer?

• Nearly thermoneutral formation reaction• Our work:

– Re-examine thermochemistry– Calculate spectroscopic constants

S. L. Widicus Weaver, D. E. Woon, B. Ruscic,and B. J. McCall, in preparation

Thermochemical CalculationsThermochemical Calculations• Active Thermochemical Tables (ATcT)

– PA0 K(O2) = 417.18 ± 0.11 kJ/mol

– PA0 K(H2) = 417.78 ± 0.01 kJ/mol

– ΔrE0 = 0.60 ± 0.11 kJ/mol = 50 ± 9 cm-1

• Ab initio calculations– ΔEe valence complete basis set (CBS) limit: +222.1 cm-1

– ΔEe core-valence contribution +28.3– harmonic vibrational ZPE correction -199.5– anharmonic vibrational ZPE correction +76.4– rotational ZPE correction -63.0

– ΔE0 net +64.3 cm-1

Branko Ruscic(Argonne)

Dave Woon(Illinois)


Interstellar Abundance of HOInterstellar Abundance of HO22++

rH°298 = 1.31 ± 0.11 kJ/mol

rG°298 = -1.75 ± 0.11 kJ/mol

)H()O()H(

2

23 nnnKT

)HO( 2n

= 2 × (10-4 cm-3) × (10-4)

N(HO2+) = n(HO2

+) L ~ (2×10-8 cm-3)(3×1018 cm) ~ 6×1010 cm-2

(likely undetectable)S. L. Widicus Weaver, D. E. Woon, B. Ruscic,and B. J. McCall, in preparation

HOHO22++ Spectroscopic Constants Spectroscopic Constants


AcknowledgmentsAcknowledgmentshttp://bjm.scs.uiuc.edu

NASA LaboratoryAstrophysics

NSF Chemistry, AMO Physics

H3+ Observations:

Takeshi Oka (U. Chicago)Tom Geballe (Gemini)

Storage Ring Measurements:Mats Larsson (Stockholm)Richard Thomas (Stockholm)

Cosmic Ray Theory:Brian Fields (Illinois)

H3+ + H2:

Kisam Park (U. Chicago → TTU)

H3+ + O:

Stephen Klippenstein (Argonne)

H3+ + O2:

Susanna Widicus Weaver (Illinois → Emory)Dave Woon (Illinois)Branko Ruscic (Argonne)

BrianTom

NickIndriolo

KyleCrabtree

MichaelWiczer

AndrewMills

[and manyothers]

Critical Research Initiative

http://astrochemistry.uiuc.edu

Spin-Modification ProbabilitySpin-Modification Probability

Total I o-H3+ + o-H2 o-H3

+ + p-H2 p-H3+ + o-H2 p-H3

+ + p-H2

o-H3+ + o-H2

5/2 1 1 0 0 0 0 0 0

3/2 4/9 1/36 0 5/12 5/9 5/9 0 0

1/2 1/9 1/9 0 0 8/9 2/9 0 2/3

o-H3+ + p-H2 3/2 0 5/12 0 1/4 1 1/3 0 0

p-H3+ + o-H2

3/2 5/9 5/9 1 1/3 4/9 10/9 0 0

1/2 8/9 2/9 0 0 1/9 17/18 1 5/6

p-H3+ + p-H2 1/2 0 2/3 0 0 1 5/6 1 1/2

Rea

ctan

ts

Products formed by Hop and Exchange

Park & Light JCP 126, 044305 (2007)

new laboratory and theoretical studies of astrophysically important reactions of h 3 +

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