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 × (Marcelino et al. 2009a) Sgr B2: ~ × (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] (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 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 HNCOHOCNHCNOHONCObs. Source Hot Core Peak~ 3× 10 5 yr Sgr B2(M) Evaporation after warm-up Surface species show strong depletion into the gas-phase. Comp. to Obs.HNCO & HOCN: best × 10 5 yr & × 10 6 yr. HCNO & HONC: abundance low during these time intervals. Warm Env Peak~ 3× 10 5 yr, Smaller 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 ×10 5 yr & ×10 5 yr; HCNO: X ~ 10 − ­ -11 ; HONC: abundance low. Lukewarm PeakNo apparent peaks. L1527 Evaporation after warm-up Insignificant. Comp. to Obs.HNCO & HCNO: good agreement after t > 100 yr; HOCN: X > when t > 2× 10 5 yr; HONC: abundance low. Cold Core Peak weak peak ~ 2× 10 5 yrNo TMC-1 & other Cold Cores Comp. to Obs. Good fit after 10 4 yr HOCN to HNCO ratio fits 5 - 5× 10 6 yr ~ 1/10 -1/500 of HNCO May be detectable.

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!