tomás gonzález lezana dep. de física atómica, molecular y ... · 2can react with deuterated...
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Ortho-para transitions of molecular hydrogen in H+ + H2 collisions
TomásGonzálezLezana
Dep.deFísicaAtómica,MolecularydeAgregadosInstitutodeFísicaFundamental(CSIC)
MADRID(ESPAÑA)
Grenoble (France) May 2017
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1. Introduction
2. Experiments and dynamics (D+ + H2, H+ + D2)
3. State-to-state study of H+ + H2
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Importance of H3+
Almost an entire separate chapter on Chemistry, Physics and Astronomy
Most abundant ionic species in hydrogen plasmas.
Crucial role in first stages of stars formation
Largely investigated:
(i) Spectroscopy(ii) PESs(iii) Reactive scattering
Both k(T) and dynamics in terms of E
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Chemical clock: The o-H2(odd j) abundance is key to estimate the age of interstellar dark clouds which lead to form stars.
D/H ratio ~ 1.5·10-5 in the vicinity of Solar System. This value is supposed to remain for HDO/H2O, N2D+/N2H+ etc…
However ND3 and CD3OH have been detected at abundances 1010, 1015 larger than expected.
Why? Grains depleted from newborn star at the center of the core.
Modelling the time for those species (D) to disappear gives age of the protostar.
Deuterium
o-H2 can react with deuterated species removing D. N2D+/N2H+ ratio increases when o-H2 abundance decrease
Study of o-H2 / p-H2 ratio !!
o-H2
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E. Roueff et al. Rate Coefficients in Astrochemistry Kluwer Academ. Pub. 73-85 (1988)
o-H2 conversion to p-H2 via collisions:
H+ + o-H2 → H+ + p-H2H3
+ + o-H2 → H3+ + p-H2
Formation of intermediate complex Statistical methods for dynamics
H + H2 ?
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A +BC → (ABC) → AB + C
å@
''''''''''''
'''2''', )(
)()(|)(|
kjv
Jkjv
Jkjv
JvjkJ
kjvvjk EpEpEp
ES
QMcalculationofprobabilitiesAbinitioPES
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2. Experiments and dynamics: (D+ + H2, H+ + D2)
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• StatisticalapproachesforJ=0-CRPfor:D++H2atE<2.1eVTakayanagi(00)H++HD :Kamisaka (02)
• Indicationsof:Short-livedcomplex
formationlowenergies(≤3eV)
Directimpulsivemechanismhigherenergies (≥4.5eV)
Krenos (74);Schiler (85,87);Ichihara (00);
What we know from Theory
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VT-SIFT:VariableTemp.SelectedIonFlowTubeHenchman81GIB:GuidedIonBeamsOchsTeloy74;Gerlich92DRIFT:DriftTubeVillinger82
Gerlichetal.PSS(2002)GerlichAdv.Chem.Phys.(1992)
What we know from Experiment
Pioneering measurements of rate coefficients
Some differences with PST approach at large E
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What we know from Experiment
E.Wrede
RovibrationallyresolvedstatedistributionsofHDareclosetothosefromtheion-moleculereaction
Attemptstodescribethingsstatistically:
Wrede etal. PCCP7 1577(2005)
H++D2 → HD+D+
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What we know from Experiment
Song etal. JCP123 074314(2005)
R.T.Skodje
Indicationsofacomplex-formingdynamicsfromtheQCTcalculation:
…andfromtheexperiment:
X.Yang
Ec = 0.526 eV
H+ + D2
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H++D2(v=0,j=0)→D++DHCarmona-Novilloetal. JCP(2008)
Betteragreementbetweentheoryandexperimentatsidewaysscattering(Θlab=52º)thanatbackwardscattering(Θlab=9º)
Ec = 0.526 eV
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AgreementwithandexactTIQMresultexceptatthestrictforward/backwardpeaks
FailureoftheQCTapproach↔ QMeffects
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TIQM rate coefficients decrease as E decreases
SQM results agree with TIQM; same discrepancies with EXP
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Rmax consistent with ρmax of the TIQM is only valid for Ec ~ 10-2 eV
Rmax 25 a0 Ec ~ 10-3 eVRmax 40 a0 Ec ~ 2 ∙10-4 eVRmax 70 a0 Ec ~ 10-4 eV
SQM
TGL,Scribano&Honvault. J.Phys.Chem.A(2014)
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Actual EXP vs Theory comparison with limits of validity for SQM and TIQM
TGL&Honvault. Int.Rev.Phys.Chem.(2014)
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SQM slightly differs from EXP beyond 0.2 eV
TIQM shows the correct trend as Ec increases
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3. State-to-state study of H+ + H2
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Ec = 440 meV
Ec = 440 meV
TGLetal.JCP125,094314 (2006)
Goodagreement(forward/backwardpeaks!) QCTfailureasJincreases
NooscillationsinSQMresult
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TGLetal.JCP125,094314 (2006)
H++H2(v = 0,j = 0)
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Numerous narrow resonances (even for the ICS!)
EQM
SQM
Prev.
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H++H2(v=0,j)→H++H2(v’=0,j’)
0 20 40 60 80 10010-12
10-11
10-10
10-9
TIQM SQM MPS Gerlich
j =0 j'=1
Rat
e C
oeffi
cien
t [cm
3 mol
ec-1 s
-1]
Temperature [K]
j =1 j'=0
Langevin type + Isotropic Mean Potential
Permutation symmetry of three protons
Still different behaviour at low T
MPS: Grozdanov&McCarrollJPCA(2012)
Still far from the TIQM rates
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Chemical clock: The o-H2(odd j) abundance is crucial to estimate the age of interstellar dark clouds which lead to form stars.
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o-H2 abundance variation with time for 3 values of cosmic ray ionization rate.
Arrows: OPR = 1, 0.1, 0.01
Pagani,Lesaffre,Honvault,Jorfi,TGL,Faure,A&A(2012)
Deuteration acceleration:
With old rates
With new rates
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O.RonceroE.Carmona-Novillo
P.G.JambrinaF.J.Aoiz,L.Bañares
E.WredeA.Trottier
P.Honvault J.-M.Launay A.Faure L.PaganiY.Scribano