Theoretical study on the formation mechanism of interstellar molecule 1-cyano-1,3-butadiene in a high-temperature interstellar environment

doi:10.3969/j.issn.1000-5641.2025.04.006

Abstract

Abstract:

The formation mechanism of interstellar molecule 1-cyano-1,3-butadiene (C₅H₅N) in high-temperature interstellar environments was explored via quantum chemical calculations. Using cyanomethyl radical (CH₂CN) and propyne/allene (C₃H₄) as reaction starting materials, the corresponding reaction potential energy surface, reaction rate, and product branch ratio were calculated at the B3LYP/cc-pVTZ level, thus deepening the study of interstellar isomers. The initial step of the reaction is the barrier-free addition of cyanomethyl radicals to the terminal carbon atoms of propyne/allene, which primarily produces E-1-cyano-1,3-butadiene and Z-1-cyano-1,3-butadiene. The research represents a class of reactions involving cyano-substituted hydrocarbons and other unsaturated hydrocarbons that has not been fully explored. The result is beneficial for clarifying the non-equilibrium reactions involved in the formation of organic nitriles, guiding researchers to have a more comprehensive understanding of the formation of organic nitriles.

Key words: reaction dynamics, 1-cyano-1, 3-butadiene, interstellar molecules

CLC Number:

O561

Yue YANG, Tao YANG, Zhihao JIN. Theoretical study on the formation mechanism of interstellar molecule 1-cyano-1,3-butadiene in a high-temperature interstellar environment[J]. J* E* C* N* U* N* S*, 2025, 2025(4): 61-68.

Figures/Tables 5

Fig.1

Fig.2

Fig.3

Table 1

Rate constants for various unimolecular reaction steps for the isomerization and dissociation of C5H6N intermediates involved in the CH2CN + CH3CCH/CH2CCH2 reactions"

Rate constants	σ^a	速率常数/ s^–1
Rate constants	σ^a	0 kJ·mol⁻¹ 0 K	0.6 kJ·mol⁻¹ 50 K	6.3 kJ·mol⁻¹ 500 K	12.5 kJ·mol⁻¹ 1000 K	62.4 kJ·mol⁻¹ 5000 K	115.0 kJ·mol⁻¹ 9224 K
m1 → mTS1 → a2, k_m1	3	5.29 × 10^–7	5.59 × 10^–7	1.23 × 10^–6	2.98 × 10^–6	9.51 × 10^–3	1.72 × 10²
a2 → mTS1 → m1, k_-m1	1	3.15 × 10^–11	3.40 × 10^–11	1.02 × 10^–10	3.34 × 10^–10	6.29 × 10^–6	3.69 × 10^–1
m2 → TS-m2-a2 → a2, k_m2-a2	1	4.03 × 10⁸	4.19 × 10⁸	5.94 × 10⁸	8.45 × 10⁸	6.85 × 10⁹	2.69 × 10¹⁰
a2 → TS-m2-a2 → m2, k_-m2-a2	1	7.20 × 10¹⁰	7.50 × 10¹⁰	1.08 × 10¹¹	1.56 × 10¹¹	1.38 × 10¹²	5.78 × 10¹²
m2 → mTS2 → a3, k_m2	1	1.28 × 10³	1.38 × 10³	3.44 × 10³	7.95 × 10³	4.86 × 10⁵	5.02 × 10⁶
a3 → mTS2 → m2, k_-m2	1	4.61 × 10⁸	4.88 × 10⁸	9.92 × 10⁸	1.87 × 10⁹	3.38 × 10¹⁰	1.51 × 10¹¹
m2 → mTS3 → p4 + H, k_m3	2	1.07 × 10^–19	1.59 × 10^–19	4.14 × 10^–17	1.53 × 10^–14	1.55 × 10²	2.54 × 10⁵
a1 → aTS1 → a2, k_a1	2	4.03 × 10^–7	4.24 × 10^–7	8.77 × 10^–7	1.99 × 10^–6	4.21 × 10^–3	5.60 × 10¹
a2 → aTS1 → a1, k_-a1	1	1.13 × 10^–11	1.22 × 10^–11	3.57 × 10^–11	1.14 × 10^–10	1.73 × 10^–6	8.36 × 10^–2
a2 → aTS2 → a3, k_a2	1	2.54 × 10³	2.73 × 10³	6.84 × 10³	1.58 × 10⁴	9.81 × 10⁵	1.02 × 10⁷
a3 → aTS2 → a2, k_-a2	1	4.58 × 10⁸	4.85 × 10⁸	9.86 × 10⁸	1.86 × 10⁹	3.35 × 10¹⁰	1.50 × 10¹¹
a2 → aTS3 → p1 + H, k_a3	2	3.09 × 10^–16	4.37 × 10^–16	5.41 × 10^–12	1.01 × 10^–11	4.07 × 10²	4.51 × 10²
a2 → aTS4 → a4, k_a4	2	1.05 × 10^–11	1.17 × 10^–11	4.96 × 10^–11	2.37 × 10^–10	8.71 × 10^–5	1.13 × 10¹
a4 → aTS4 → a2, k_-a4	1	3.60 × 10^–7	3.90 × 10^–7	1.22 × 10^–6	4.34 × 10^–6	2.78 × 10^–1	1.13 × 10⁴
a2 → aTS8 → a6, k_a8	1	1.18 × 10¹²	1.18 × 10¹²	1.20 × 10¹²	1.22 × 10¹²	1.36 × 10¹²	1.47 × 10¹²
a6 → aTS8 → a2, k_-a8	1	1.25 × 10¹²	1.25 × 10¹²	1.29 × 10¹²	1.32 × 10¹²	1.55 × 10¹²	1.74 × 10¹²
a6 → aTS9 → p2 + H, k_a9	2	2.82 × 10^–10	2.60 × 10^–10	1.17 × 10^–10	5.04 × 10^–10	1.25 × 10^–4	1.42 × 10²
a3 → aTS5 → a5, k_a5	2	2.13 × 10^–8	2.27 × 10^–8	5.82 × 10^–6	1.64 × 10^–7	1.39 × 10^–3	5.68 × 10¹
a5 → aTS5 → a3, k_-a5	1	3.38 × 10^–12	3.68 × 10^–12	1.21 × 10^–11	4.40 × 10^–11	1.70 × 10^–6	1.99 × 10^–1
a5 → aTS6 → p3 + H, k_a6	2	1.60 × 10⁷	1.66 × 10⁷	2.75 × 10⁷	4.49 × 10⁷	7.53 × 10⁸	4.81 × 10⁹
a4 → aTS7 → a5, k_a7	1	1.11 × 10⁶	1.22 × 10⁶	3.88 × 10⁶	9.81 × 10⁶	3.53 × 10⁸	1.79 × 10⁹
a5 → aTS7 → a4, k_-a7	1	9.32 × 10²	1.05 × 10³	4.74 × 10³	1.69 × 10⁴	4.59 × 10⁶	9.22 × 10⁷
a3 → aTS5 → a5, k_a5	2	2.13 × 10^–8	2.27 × 10^–8	5.82 × 10^–6	1.64 × 10^–7	1.39 × 10^–3	5.68 × 10¹

Table 1

Table 2

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Products	产物分支比
Products	121.5 kJ·mol⁻¹ 9744 K	122 kJ·mol⁻¹ 9787 K	123 kJ·mol⁻¹ 9866 K	124 kJ·mol⁻¹ 9948 K	125 kJ·mol⁻¹ 10028 K	126 kJ·mol⁻¹ 10105 K
CH₂CN + propyne
p1: E-1-cyano-1,3-butadiene + H	67.561	67.549	67.384	67.249	67.059	66.992
p2: Z-1-cyano-1,3-butadiene + H	32.216	32.317	32.356	32.463	32.653	32.720
p3: pyridine + H	0	0	0	0	0.001	0.001
p4: gauche-E-1-cyano-1,3-butadiene + H	0.124	0.134	0.260	0.288	0.287	0.287
CH₂CN + allene
p1: E-1-cyano-1,3-butadiene + H	100	51.967	51.958	51.875	51.813	51.737
p2: Z-1-cyano-1,3-butadiene + H	0	48.033	48.042	48.124	48.185	48.251
p3: pyridine + H	0	0	0	0.001	0.002	0.002
p4: gauche-E-1-cyano-1,3-butadiene + H	0	0	0	0	0	0