星际介质中预生物分子的化学建模研究 Chemical Modeling Studies of Interstellar Prebiotic Molecules 全冬晖 July 28th, 2018

Outline Interstellar Medium Prebiotic Molecules Detection Ethanimine Modeling Cyanomethanimine Modeling Future Work

Interstellar Medium

Detected Interstellar Molecules 2 atoms H2 CH CH+ NH OH OH+ HF HCl SH C2 CN CO CO+ CF+ CP CS N2? NO PN NS SiN SO SO+ PO SiO AlO FeO? AlF NaCl AlCl KCl SiS O2 3 atoms H3+ CH2 NH2 H2O HDO H2S CCH HCN HNC HCO+ HOC+ HCO N2H+ HCP HNO HCS+ C3 C2O OCS N2O SO2 SiCN SiNC AlNC MgCN MgNC NaCN HCP CCP 4 atoms CH3 NH3 H3O+ H2CO HCCH HCCO H2CN HCNH+ H2CS C3H c-C3H HCCN HNCO HOCN HCNO HOCO+ HNCS HSCN C3N C3O C3S c-SiC3 C3N- PH3? 5 atoms CH4 SiH4 H2COH+ H2CNH C3H2 c-C3H2 CH2CN NH2CN CH2CO HCOOH C4H C4H- HC3N HC2NC HNCCC C5 C4N C4Si HCOCN 6 atoms C2H4 CH3OH CH3SH CH3CN CH3NC CH2CNH NH2CHO c-C4H2 C4H2 HC2CHO c-C3H2O HC3NH+ C5O C5N HC4N C5H HC4H? C5N- 7 atoms CH3CHO CH3NH2 CH3CCH C2H3OH c-CH2OCH2 C2H3CN HC5N C6H C6H- 8 atoms C2H6 HCOOCH3 CH3COOH HOCH2CHO C2H3CHO CH3C3N CH2CCHCN C7H H2NCH2CN (NH2)2CO CH3CHNH 9 atoms CH3CHCH2 CH3OCH3 CH3CONH2 CH3C4H C8H C8H- HC7N C2H5CN C2H5OH C2H5SH 10+ atoms C2H5CHO CH3COCH3 (CH2OH)2 CH3C5N CH3C6H HC9N C2H5OCHO C6H6 C3H7CN HC11N, PAHs

Detection of Interstellar Prebiotic molecules GBT PRIMOS survey reported both E- and Z- ethanimine detection. Stable isomer is more abundant. Physical conditions unclear.

Detection of Ethanimine Isomers Toward Sgr B2(N) E-CH3CHNH N = 7×1013 cm-2 Z-CH3CHNH N = 2.3×1013 cm-2 Trot = 6 K

Detection of Interstellar Prebiotic molecules HNCNH Observation toward Sgr B2 Isomer of NH2CN Column Density: 2×1013 cm-2 HNCHCN E-, Z-, and N-isomers Column Density: E- 1.5×1013 cm-2 CH3NCO Observation toward Sgr B2 (and comet) Column Density: ～2×1013 cm-2

Modeling Method – Kinetics Model A1 + B1 → C A2 + B2 → C + E D1 + C → P1 D2 + C→ P2 + P3 C → P4 Rdes = k3 [D1] [C] + k4 [D2] [C] + k5 [C] Rform = k1 [A1] [B1] + k2 [A2] [B2] d[C]/dt = Rform – Rdes = k1 [A1] [B1] + k2 [A2] [B2] - k3 [D1] [C] - k4 [D2] [C] - k5[C] dni / dt = ΣjΣlkjlnjnl + Σokiono − Σpkipni − Σmkimninm

Modeling Method – Gas-grain Model Accretion Small Molecules Dust Particle Desorption Products

Ethanimine Modeling – Gas-grain Models Modified OSU gas-grain network: ~700 species, >7000 reactions. Surface species & surface reactions included Physical parameters: vary, see next slides Elemental abundances: low-metal; O-rich

Ethanimine Modeling – Physical Parameters N3Z1 N4Z1 N5Z1 N6Z1 N3Z2 N4Z2 N5Z2 N6Z2 nH (cm-3) 2×103 2×104 2×105 2×106 Tasym (K) (FT10~FT200*) 10~200 ζ (s-1) 1.3×10−17 1.3×10−16 Av 10 d/g 0.01 aRRK UV Factor 1

Ethanimine Modeling – Temperature Settings

Elemental Abundances Species O-rich He 6.00 × 10-2 N 2.14 × 10-5 O 1.76 × 10-4 H2 5.00 × 10-1 C+ 7.30 × 10-5 S+ 8.00 × 10-8 Si+ 8.00 × 10-9 Fe+ 3.00 × 10-9 Na+ 2.00 × 10-9 Mg+ 7.00 × 10-9 P+ Cl+ 4.00 × 10-9

Ethanimine Modeling Results

Ethanimine Modeling Results – Temperature Effects

Ethanimine Modeling Results – Density Effects

Ethanimine Modeling Results – Zeta Effects

Ethanimine Modeling Results – E- and Z- Isomers

Ethanimine Modeling Results - Discussion Ethanimine desorption becomes effective at FT≥90K, and complete desorption occurs at FT≥110K. In the higher cosmic ray ionization model, a slightly higher temperature of FT ≥ 97K is required. All explored densities can account for ethanimine detection while higher densities will bring non-thermal desorption peaks to earlier time. E-ethanimine is more abundant than Z-isomer due to slower destruction reactions.

Cyanomethanimine Modeling HNCHCN Observation toward Sgr B2 E-, Z-, and N-isomers Column Density: E- 1.5×1013 cm-2

Future Work HNCNH CH3NCO Observation toward Sgr B2 Isomer of NH2CN Column Density: 2×1013 cm-2 CH3NCO Observation toward Sgr B2 (and comet) Column Density: ～2×1013 cm-2

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