Donghui Quan& Eric Herbst

The Ohio State University

OutlineObservational ResultsModeling MethodEssential ReactionsResults and DiscussionConclusion

CHNO Isomers in the UniverseHNCOTMC-1: ~ 5 × 10-10 (Marcelino et al.

2009a)Sgr B2: ~ 0.5-5× 10-9 (Churchwell et al. 1986; Liu & Snyder

1999; Brünken et al. 2009a,b)

HOCNSgr 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)

HCNOTMC-1 : < 0.3% of [HNCO] (Marcelino et al.

2009a)Cold Cores : ~ 2% of [HNCO] (Marcelino et al. 2009a)L1527 : ~ 3% of [HNCO] (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 ReactionsGas 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 ReactionsHNCO: 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 resultsMODEL   HNCO HOCN HCNO HONC Obs.

Source  

Hot Core 

Peak ~ 3× 105 yr   

Sgr B2(M)

 

 Evaporation after warm-up

Surface species show strong depletion into the gas-phase.

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.

  

Warm Env 

Peak ~ 3× 105 yr , Smaller

 ~ 3× 105 yr , Smaller

 No No  Env. Sgr B2 (M) &

(N), Sgr

B2(OH) 

Evaporation after warm-up

Surface species show fair depletion into the gas-phase.

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.

  

Lukewarm

Peak No apparent peaks.    

L1527Evaporation

after warm-up Insignificant.

Comp. to Obs. HNCO & HCNO: good agreement after t > 100 yr;HOCN: X > 10-11 when t > 2× 105 yr; HONC: abundance low.

 Cold Core

Peak  weak peak~ 2× 105 yr No  No No

 TMC-1 &

other Cold Cores

Comp. to Obs.

Good fit after 104 yr

HOCN to HNCO ratio

fits obs. @105 - 5× 106 yr

~ 1/10 -1/500 of HNCO

May be detectable.

An analogous system – CHNS Isomers

ConclusionsCHNO 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.

AcknowledgementDr. Yoshihiro Osamura

Dr. David Woon

Dr. Sandra Brünken

NSF funding

Thank you all!