1. 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

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

3. Interstellar Medium

5. 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

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

7. 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

8. 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

9. 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

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

11. 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

12. 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

13. Ethanimine Modeling – Temperature Settings

14. 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

16. Ethanimine Modeling Results

17. Ethanimine Modeling Results – Temperature Effects

18. Ethanimine Modeling Results – Density Effects

19. Ethanimine Modeling Results – Zeta Effects

20. Ethanimine Modeling Results – E- and Z- Isomers

21. 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.

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

23. 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

24. Questions？