Donghui Quan
& Eric Herbst
The Ohio State University
Outline
 Observational Results
 Modeling Method
 Essential Reactions
 Results and Discussion
 Conclusion
CHNO Isomers in the Universe
 HNCO
TMC-1: ~ 5 × 10-10
Sgr B2: ~ 0.5-5× 10-9
(Marcelino et al. 2009a)
(Churchwell et al. 1986; Liu & Snyder 1999;
Brünken et al. 2009a,b)
 HOCN
Sgr B2(OH): ~ 0.4% of [HNCO]
(Brünken et al. 2009b; Turner 1991)
Sgr B2 (M) : ~ 1.5% of [HNCO](Brünken et al. 2009a,b; Marcelino et al. 2009b)
TMC-1
: ~ 1% of [HNCO]
(Brünken et al. 2009a,b )
Cold Cores: ~ 2% of [HNCO]
(Marcelino et al. 2009b)
 HCNO
TMC-1
: < 0.3% of [HNCO]
Cold Cores : ~ 2% of [HNCO]
L1527
: ~ 3% of [HNCO]
(Marcelino et al. 2009a)
(Marcelino et al. 2009a)
(Marcelino et al. 2009a)
Why different?
Modeling Method – Gas-grain Modeling
 Four models: hot core, warm envelope, lukewarm, cold core.
 Gas-grain network: ~700 species, >6000 reactions.
 3-phase warm-up: T starts at low constant value, increases to
and stays at higher value after certain time-point.
 Non-thermal desorption: driven by energies from exothermic
surface reactions.
Modeling Method – Physical Conditions and
Initial Abundances
Essential Formation Reactions
 Gas phase:
NCO+ + H2 -> HNCO+ + H,
HNCO+ + H2 -> HNCOH+/H2NCO+ + H,
HNCOH+ + e- -> HNCO/HOCN + H,
H2NCO+ + e- -> HNCO + H.
HCNO & HONC can be produced similarly,
plus: CH2 + NO -> HCNO + H.
 Grain surface (J):
N + HCO -> NCO + H,
JH + JNCO -> JHNCO/JHOCN.
JC + JNO -> JCNO,
JH + JCNO -> JHCNO/JHONC.
Essential Destruction Reactions
 HNCO:
cations, cosmic ray indirect destruction, photon dissociation etc.
 HOCN:
cations, cosmic ray indirect destruction, photon dissociation etc,
C + HOCN -> CO + HCN, HCO + CN, H + OCNC, and OH + CNC,
O + HOCN -> OH + NCO.
 HCNO:
cations, cosmic ray indirect destruction, photon dissociation etc,
C + HCNO -> C2H + NO.
 HONC:
cations, cosmic ray indirect destruction, photon dissociation etc,
O + HONC -> O2H + CN.
Modeling results – Hot Core Model
• Peaks occur after
warm-up;
• HNCO & HOCN:
two time periods of
best agreement;
• HCNO & HONC:
abundances low.
Modeling results
MODEL
Hot Core
Warm Env
Lukewarm
Cold Core
HNCO
HOCN
HCNO
HONC
Peak
~ 3× 105 yr
Evaporation after
Surface species show strong depletion into the gas-phase.
warm-up
Comp. to Obs.
HNCO & HOCN: best fit @1.2 - 1.5 × 105 yr & 1.1 - 1.6 × 106 yr.
HCNO & HONC: abundance low during these time intervals.
Peak
No
No
~ 3× 105 yr ,
~ 3× 105 yr ,
Smaller
Smaller
Evaporation after Surface species show fair depletion into the gas-phase.
warm-up
Comp. to Obs.
HNCO & HOCN: best fit @1.8-2.0 ×105 yr & 6.6-19×105 yr;
HCNO: X ~ 10−12- 10-11; HONC: abundance low.
Peak
No apparent peaks.
Evaporation after
Insignificant.
warm-up
Comp. to Obs.
HNCO & HCNO: good agreement after t > 100 yr;
HOCN: X > 10-11 when t > 2× 105 yr; HONC: abundance low.
Peak
weak peak
No
No
No
~ 2× 105 yr
Comp. to Obs.
HOCN to HNCO
Good fit after ratio fits obs. @105 ~ 1/10 -1/500
May be
4
6
10 yr
of HNCO
detectable.
- 5× 10 yr
Obs.
Source
Sgr B2(M)
Env. Sgr
B2 (M) &
(N),
Sgr
B2(OH)
L1527
TMC-1 &
other Cold
Cores
An analogous system – CHNS
Isomers
Conclusions
 CHNO isomers are produced by a combination of
surface and gas-phase chemistry.
 In general, our models are able to reproduce both the
abundance of the dominant isomer HNCO and the
minor isomer, HCNO or HOCN.
 CHNS isomers present another interesting case of how
astronomical environments lead to the production and
destruction of differing isomers.
Acknowledgement
 Dr. Yoshihiro Osamura
 Dr. David Woon
 Dr. Sandra Brünken
 NSF funding
 Thank you all!