Chemistry of C<sub>2</sub>S and C<sub>3</sub>S in L1544 with NSRT

Rong Ma; Xiaohu Li; Donghui Quan; Juan Tuo; Ryszard Szczerba; Jarken Esimbek; Jianjun Zhou; Wasim Iqbal; Jixing Ge; Gleb Fedoseev; Xia Zhang; Yanan Feng; Yong Zhang; Tao Yang; Xuan Fang; Yihan Wu; Fangfang Li; Zhenzhen Miao; Xindi Tang; Dalei Li; Yuxin He; Gang Wu; Weiguang Ji; Chuan-Lu Yang

doi:10.1088/0256-307X/42/1/019701

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Chemistry of C₂S and C₃S in L1544 with NSRT

Rong Ma^{1, 2},
Xiaohu Li^{1, 3, 4, ,},
Donghui Quan^{1, 5, ,},
Juan Tuo^{1, 3},
Ryszard Szczerba^{1, 3},
Jarken Esimbek^{1, 3},
Jianjun Zhou^{1, 3},
Wasim Iqbal^{1, 3},
Jixing Ge^{1, 3},
Gleb Fedoseev^{1, 3},
Xia Zhang^{1, 3},
Yanan Feng^{1, 2},
Yong Zhang^{1, 6, 7},
Tao Yang^{1, 8},
Xuan Fang^{1, 6, 9},
Yihan Wu^{1, 3},
Fangfang Li^{1, 2, 3},
Zhenzhen Miao^{1, 3},
Xindi Tang^{1, 3},
Dalei Li^{1, 3},
Yuxin He^{1, 3},
Gang Wu^{1, 3, 10},
Weiguang Ji^{1, 3},
Chuan-Lu Yang^{1, 11}

1.
Xinjiang Astronomical Observatory, Chinese Academy of Sciences, Urumqi 830011, China
2.
University of Chinese Academy of Sciences, Beijing 100049, China
3.
Xinjiang Key Laboratory of Radio Astrophysics, Urumqi 830011, China
4.
Key Laboratory of Radio Astronomy and Technology, Chinese Academy of Sciences, Beijing 100101, China
5.
Research Center for Astronomical Computing, Zhejiang Laboratory, Hangzhou 311100, China
6.
Laboratory for Space Research, Faculty of Science, The University of Hong Kong, Hong Kong, China
7.
School of Physics and Astronomy, Sun Yat-sen University, Guangzhou 510275, China
8.
State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China
9.
National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China
10.
Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
11.
School of Physics and Optoelectronic Engineering, Ludong University, Yantai 264025, China

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Corresponding author:
Xiaohu Li, Email: xiaohu.li@xao.ac.cn

Donghui Quan, Email: donghui.quan@zhejianglab.com

Received Date: September 20, 2024

Accepted Date: November 21, 2024

Published Date: December 31, 2024

Abstract

Abstract

Abstract Sulfur-bearing species are widely utilized to investigate the physical structure of star-forming regions in interstellar media; however, the underlying sulfur chemistry in these environments remains poorly understood. Therefore, further studies of S-bearing species are fundamentally important, as they can enhance our understanding of the physical evolution of star-forming regions. This study presents observations of C₂S and C₃S in L1544, acquired using the Nanshan 26-m radio telescope, along with simulations of their chemical behavior using a one-dimensional physical model. The simulation results reveal significant radial variations in the column densities of C₂S and C₃S. Additionally, the column densities of both molecules are found to be sensitive to the cosmic ray ionization rate at several radial positions, while variations in the C/O ratio have comparatively minimal impact on L1544.

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1. Introduction. The recent detection of sulfur-bearing carbon chains in TMC-1 and complex organosulfur molecules in the material of comet 67P/Churyumov-Gerasimenko has brought the chemistry of sulfur-bearing species to the forefront of modern astrochemistry. With a cosmic abundance relative to hydrogen (H) of 1.73 × 10⁻⁵,^[1] sulfur (S) one of the most enigmatic elements in astrochemistry is a vital component of many proteins, alongside more abundant elements, such as hydrogen, carbon (C), oxygen (O), and nitrogen (N).^[2] Despite extensive studies of sulfur chemistry in interstellar media (ISM), its complexity, especially in star-forming molecular clouds, remains unresolved. In diffuse ISM regions and photon-dominated regions (PDRs), observed sulfur abundances are close to cosmic values.^[3,4] However, in dense molecular clouds, gas-phase sulfur abundance is observed to be only about 0.1% or 1% of the cosmic sulfur abundance,^[5] indicating depletion factors as high as three orders of magnitude.^[6,7] A major unresolved question is the primary reservoir of sulfur in the ISM. Theoretical models suggest that H₂S could be the most significant sulfur reservoir;^[8] however, only OCS and SO₂ have been detected in ice mantles.^[9,10]

Pre-stellar core L1544, located in the Taurus molecular cloud at a distance of 170 pc,^[11] is characterized by high central densities of approximately 10⁶–10⁷ cm⁻³ and a central temperature of about 6 K.^[12,13] This chemically rich core exhibits spatial inhomogeneities in molecular emission distributions.^[14,15] Reference [7] examined the sulfur chemistry of L1544, predicting strong radial variations in the abundance of sulfur species. In this study, we present observations of C₂S and C₃S toward L1544 using the Nanshan 26-m radio telescope (NSRT-26 m) at the Xinjiang Astronomical Observatory, complemented by astrochemical modeling to explore sulfur chemistry under varying physical conditions, such as the carbon-to-oxygen (C/O) ratio and cosmic ray ionization rate.

To understand sulfur chemistry in the ISM, it is essential to validate models by observing sulfur-bearing molecules across diverse physical conditions. However, certain conditions, such as the C/O ratio, remain poorly constrained due to observational limitations. Volatile abundances of carbon and oxygen (in both gas and ice phases) often have uncertainties of about a factor of two,^[16,17] leading to substantial discrepancies in astrochemical model predictions.^[18] Simulations by Ref. [19] showed that the gas-phase abundance of sulfur-bearing species in Taurus Molecular Clouds (TMC-1) is highly sensitive to the C/O ratio. Additionally, cosmic rays (CRs) significantly influence the chemistry and physics of cold, dense star-forming regions.^[20] In such environments, CRs act as primary ionizing agents, driving the complex chemistry of molecular ions. CRs also influence the ionization fraction, which regulates the coupling between the gas and interstellar magnetic fields, as well as the heating of the gas.^[21] In this study, the cosmic ray ionization rate is denoted by ζ_CR. Reference[22] provides an upper limit of approximately ζ_CR ≈ 10⁻¹⁶ s⁻¹ based on gas temperature measurements in L1544. Model results from Ref. [21] exclude high cosmic-ray ionization rates (>10⁻¹⁶ s⁻¹) and estimate the average cosmic-ray ionization rate to be approximately ζ_CR ≈ 3 × 10⁻¹⁷ s⁻¹ in the low-mass prestellar core L1544. These findings suggest that the cosmic-ray ionization rate in molecular clouds or prestellar cores may differ from the standard value of ζ_CR ≈ 1.3 × 10⁻¹⁷ s⁻¹ typically used in astrochemical models.

2. Observations. Single-point observations of the prestellar core L1544 were conducted using the NSRT-26 m telescope at the Xinjiang Astronomical Observatory, Chinese Academy of Sciences (CAS), in April 2021. The J2000 coordinates of the observation are RA = 05h04m16.60s, Dec = 25°10′48.00″. The J_N = 2₁–1₀ transition of C₂S and the J = 4–3 transition of C₃S were observed, with the spectral line parameters listed in Table 1. Parameters for C₂S and C₃S were obtained from the Cologne Database for Molecular Spectroscopy (CDMS^*^[23]). During the observations, the system temperature was maintained at ∼40 K. The receiver’s back end utilized a Digital Filter Bank with 8192 channels and 64 MHz bandwidth, providing a frequency resolution of 7.8125 kHz, a velocity resolution of 104.8 m⋅s⁻¹ at 22.344 GHz and 101.3 m⋅s⁻¹ at 23.122 GHz. The half-power beam widths (HPBW) were 109″ and 105″ for C₂S and C₃S respectively. The antenna temperature ( $T_{A}^{*}$ ) is related to the main beam brightness temperature (T_mb) via the main beam efficiency (η), i.e. $T_{mb} = T_{A}^{*} / η$ ; the value of η for NSRT is approximately 0.6. Observations were performed in position-switching mode, with an integration time of three minutes for each on-source and off-source scan. The total integration time for each molecule was 48 minutes, excluding telescope overhead for position switching. The calibration uncertainty (%) of the NSRT-26 m was 14%.^[24] Data processing for C₂S and C₃S was performed using CLASS, a component of the GILDAS software suite^†.

Table 1. Spectral line parameters of C₂S and C₃S detected in L1544.

Molecule	Transition	ν	Sμ²	B	E_u	rms	T_mb	∫T_mbdv	V_LSR	FWHM
Molecule	Transition	(MHz)	(Debye²)	(MHz)	(K)	(mK)	(K)	(K⋅km⋅s⁻¹)	(km⋅s⁻¹)	(km⋅s⁻¹)
C₂S	J_N = 2₁–1₀	22344.0308	16.43636	6477.75	1.60598	19.17	0.562	0.211 (0.030)	7.160 (0.005)	0.353 (0.010)
C₃S	J = 4–3	23122.9836	54.88343	2890.38	2.77441	23.29	0.146	0.057 (0.010)	7.117 (0.023)	0.369 (0.050)
Note. ∫T_mbdv is the integral intensity, V_LSR is the local standard of rest radial velocity, and FWHM is the full-width at half-maximum, the values in parentheses are the corresponding derived errors. The parameters of the molecules are taken from the CDMS.^[23]

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3. Results. For the C₂S and C₃S lines, the Gaussian fitting routine in CLASS was used to derive line parameters, including the main beam brightness temperature (T_mb), integrated intensity (W = ∫T_mbdv), local standard of rest radial velocity (V_LSR), and full width at half maximum (FWHM). These results are summarized in Table 1. The observed spectral lines for C₂S and C3S are shown in Fig. 1. The error in ∫T_mbdv was calculated using $σ_{w} = \sqrt{{(cal \times W)}^{2} + {[rms \times \sqrt{2 \times FWHM \times Δ V}]}^{2}}$ , where cal represents the calibration uncertainty, ΔV is the velocity resolution, and rms is derived from regions free of obvious spectral lines.

Fig. 1. The detected molecular emissions for C₂S and C₃S in L1544 are illustrated in Fig. 1. The black line represents the observed spectral line profile, and the red line corresponds to the Gaussian fit. The molecule names and rotational transitions are indicated in the upper right corners of the respective panels.

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Assuming local thermodynamic equilibrium (LTE) conditions and optical thinness of C₂S and C₃S, the column densities of these species were derived using the following equations:^[25,26]

$N_{tot} = \frac{3 k}{8 π^{3} ν} \frac{Q (T_{ex})}{S μ^{2}} \frac{e^{E_{u} / k T_{ex}} J_{ν} (T_{ex})}{J_{ν} (T_{ex}) - J_{ν} (T_{bg})} \int T_{mb} d v,$

(1)

where k, Sμ², E_u, and ν represent the Boltzmann constant, the product of the total torsion-rotational line strength and the square of the electric dipole moment, the upper level energy, and the rest frequency of the line, respectively. Q(T_ex) denotes the partition function, which was estimated as follows:

$Q (T_{ex}) = \frac{k T_{ex}}{h B} e^{(h B / 3 k T_{ex})},$

(2)

where T_ex, h, and B are the excitation temperature, Planck’s constant, and rigid rotor rotation constant, respectively. Sμ², B, and E_u are obtained from CDMS^[23] and are listed in Table 1. T_bg (2.73 K) represents the cosmic background temperature. J_ν(T) is the equivalent Rayleigh-Jeans temperature defined by

$J_{ν} (T) = (\frac{h ν}{k}) {[e^{(h ν / k T)} - 1]}^{- 1} .$

(3)

The calculated column densities for C₂S and C₃S are listed in Table 2. The error in the column density (σ_{N_tot}) was calculated using σ_{N_tot} = σ_WN_tot/W. Reference [27] observed C₂S (J_N = 2₁–1₀) and C₃S (J = 4–3) in L1544 with the Nobeyama-45 m telescope, deriving a column density of 1.8 × 10¹³ cm⁻² for C₂S and 4.2 × 10¹² cm⁻² for C₃S, assuming excitation temperatures of 5 K and 5.5 K, respectively. Ref. [7] reported lower column densities for both C₂S and C₃S compared to Ref. [27], indicating discrepancies in the derived values. We determined a C₂S column density of (4.3±0.6) × 10¹² cm⁻² at an excitation temperature of 4.9 K and a C₃S column density of (8.7±1.6) × 10¹¹ cm⁻² at an excitation temperature of 7.9 K. Observations of the same molecular transitions using different telescopes can yield varying column densities, potentially due to the effect of the telescope’s beam dilution factor, which was not accounted for in either our analysis or that of Ref. [27]. Additionally, differences in the calculation methods may contribute to variations in the derived column densities. The previous results for these molecules’ column densities are summarized in Table 2. Except for the results from Ref. [27], our findings are generally consistent with other determinations.

Table 2. Column densities of C₂S and C₃S detected in L1544 in this work and from the literature.

Molecule	T_ex	N	Note
Molecule	(K)	(cm⁻²)	Note
C₂S	4.9±0.2^*	(4.36±0.62) × 10¹²	This work
	5	1.8 × 10¹³	Ref. [27]
		(0.96–4.4) × 10¹²	Ref. [28]
	4.9±0.2	(7.5±1.3) × 10¹²	Ref. [7]
	8.8±0.19	(4.9±0.39)× 10¹²	Ref. [29]
C₃S	7.9±0.2^*	(8.73±1.56)× 10¹¹	This work
	5.5	4.2× 10¹²	Ref. [27]
	7.9±0.2	(8.8± 0.7)× 10¹¹	Ref. [7]
	9.6±0.11	(1.2±0.6)× 10¹²	Ref. [29]
* The value of T_ex is taken from Ref. [7].

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4. Models. The physical model of L1544 is based on a one-dimensional quasi-equilibrium Bonnor–Ebert sphere developed by Ref. [30], which reproduces the observed C¹⁸O, H₂O, and N₂H⁺ lines. The model provides radius-dependent values for H₂ density, gas temperature (T_gas), dust temperature (T_dust), and visual extinction (A_V), as shown in Fig. 2.

Fig. 2. The employed physical models in this work, extracted from the work of Keto and Caselli (2010). The number density of H₂ [n(H₂), top panel, black line], visual extinction (A_V, top panel, red line), gas temperature (T_gas, bottom panel, blue line), and dust temperature (T_dust, bottom panel, green line) are plotted as a function of radius from the central core towards the edge of the cloud.

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In this study, we utilized the Nautilus three-phase model,^[31] which accounts for the gas phase, the dust surface (top two layers of ice mantles), and the bulk of the ice mantles. The chemical network was derived from Ref. [32], which extended the sulfur chemical network to explain the observed abundances of sulfur-containing species in TMC-1. Reference[7] demonstrated that significant sulfur depletion is required to reproduce the observations of the prestellar core L1544, leading us to adopt an S/H ratio of 8.0 × 10⁻⁸. Recent studies of dark clouds^[32,33] employed a C/O ratio of 0.7 or lower to explain the observed abundances of sulfur-bearing species. We modeled the chemical composition by varying the C/O ratio through adjustments in the C⁺ abundance, presenting models with C/O ratios of 0.5, 0.7, and 0.9. The initial conditions are listed in Table 3. For the cosmic ray ionization rate, we tested three scenarios: (1) the standard value commonly used in astrochemical models, ζ_CR ≈ 1.3 × 10⁻¹⁷ s⁻¹; (2) an average cosmic ray ionization rate of ζ_CR ≈ 3 × 10⁻¹⁷ s⁻¹ for L1544 derived by Ref. [21]; and (3) a high cosmic ray ionization rate of ζ_CR ≈ 1 × 10⁻¹⁶ s⁻¹. We simulated the chemical evolution over 10⁶ years and compared the results of our chemical modeling with observational data for C₂S and C₃S in L1544. Column densities were calculated using a method adapted from Ref. [7].

Table 3. The initial elemental abundances used in our models.

Species	n_i/n_H	Reference
H₂	0.5
He	9.0× 10⁻²	[36]
C⁺	1.7× 10⁻⁴	[37]
N	6.2× 10⁻⁵	[37]
O	2.4× 10⁻⁴	[38]
S⁺	8.0× 10⁻⁸	[7]
Si⁺	8.0× 10⁻⁸	[39]
Fe⁺	3.0× 10⁻⁹	[39]
Na⁺	2.0× 10⁻⁹	[39]
Me⁺	7.0× 10⁻⁹	[39]
P⁺	2.0× 10⁻¹⁰	[39]
Cl⁺	1.0× 10⁻⁹	[39]
F	6.7 × 10⁻⁹	[40]

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Figures 3 and 4 show the column density profiles of C₂S and C₃S calculated using different models. Four time steps (1.00 × 10⁵, 2.78 × 10⁵, 4.64 × 10⁵, and 1.00 × 10⁶ years) were selected within the range of 10⁵–10⁶ years, based on the models in Ref. [34] and Ref. [35] models, as these simulations extend beyond 10⁵ years to align with observations. The observed column densities of C₂S and C₃S, presented in Fig. 3 and 4, fall within the range summarized in Table 2 (indicated by the gray shaded area), while the black dashed line represents the column density calculated in this study.

Fig. 3. The column density of C₂S is presented as a function of radius from the central core to the cloud edge at four selected representative evolutionary time points. The results for various models are shown using different colors, with each color representing simulations based on distinct cosmic-ray ionization rate models. The solid line corresponds to C/O = 0.5, the dashed line represents C/O = 0.7, and the dotted line indicates C/O = 1.0. The black dashed line reflects the column density calculated in this study, the black shaded area represents the uncertainty, while the gray shaded area denotes the range of column densities summarized in Table 2.

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Fig. 4. Same as Fig. 3 but for the molecule of C₃S.

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The modeling results demonstrate significant radial variation in the column densities of C₂S and C₃S. For both molecules, column densities peak at distances between 5 × 10³ and 10⁴ AU across different models at ages exceeding 1 × 10⁵ years. In these models, the primary formation reaction routes for C₂S are as follows:

${HC}_{2} S^{+} {+ e}^{-} \to {H + C}_{2} S,$

(4)

${HC}_{3} S^{+} {+ e}^{-} \to {CH + C}_{2} S .$

(5)

Near the 10⁴ AU position, C₂S can also be produced by the following reaction:

$C + HCS \to C_{2} S + H .$

(6)

HCS is formed via the reaction of C with H₂S, which itself is produced on dust grains and subsequently released into the gas phase. The main destructive reactions of C₂S occur at distances ranging from 10³ to 10⁵ AU.

$C_{2} {S + C}^{+} \to {S + C}_{3}^{+},$

(7)

$C_{2} {S + C}^{+} \to {C + C}_{2} S^{+},$

(8)

$C_{2} {S + H}_{3}^{+} \to H_{2} {+ HC}_{2} S^{+} .$

(9)

For C₃S, the main formation reactions at all positions areas follows:

${HC}_{3} S^{+} {+ e}^{-} \to {H + C}_{3} S,$

(10)

C₃S is mainly destroyed by C⁺ at positions ranging from 10³ to 10⁵ AU.

$C_{3} {S + C}^{+} \to {S + C}_{4}^{+},$

(11)

$C_{3} {S + C}^{+} \to {CS + C}_{3}^{+},$

(12)

$C_{3} {S + C}^{+} \to C_{3} {+ CS}^{+} .$

(13)

When comparing the simulation results (represented by the red, green, and blue lines) with the observations (indicated by the black dashed horizontal line), we find that at an age of 1 × 10⁵ years, the column density of C₂S matches the observational values at the 10⁴ AU position for each model. In contrast, for C₃S, the column density reaches observational values near 5 × 10³ AU for some models at the same age of 1 × 10⁵ years. By 2.78 × 10⁵ years, the column densities of both C₂S and C₃S align with observational values at similar positions across different models. At a cloud age of 10⁶ years, each model shows a peak column density for C₂S and C₃S at 10⁴ AU. These modeling results suggest that C₂S and C₃S likely originate from regions approximately 2 × 10³ to 10⁴ AU from the central core, corresponding to the external layer of the pre-stellar core.

The column densities of C₂S and C₃S were found to be relatively insensitive to variations within the chosen range of C/O ratios. Notably, only at distances around 10⁴ AU do the models with C/O ratios of 0.5 and 0.7 show significant differences, with the column densities calculated for the C/O = 0.7 model being higher than those for the C/O = 0.5 model. Additionally, models with C/O ratios of 0.7 and 1.0 yield nearly identical results for both C₂S and C₃S.

Furthermore, the cosmic ray ionization rate may influence the column densities of C₂S and C₃S, particularly at ages less than 4.64 × 10⁵ years and a distance of 10⁴ AU. A higher cosmic-ray ionization rate results in increased column densities of C₂S and C₃S. CRs are the primary ionizers of gases and influence the chemical properties by generating ions and electrones. The ionization of hydrogen molecules by CRs produces ions,

${CR + H}_{2} \to H_{2}^{+} {+ e}^{-} + CR,$

(14)

both C₂S and C₃S molecules were produced through the reaction of ions with e⁻ [Eqs. (4), (5), and (10)]. Therefore, a higher cosmic ray ionization rate leads to an increased column density of these molecules. Recent theoretical models have characterized the increase in CRs decay with increasing density.^[21] Given that the column density of H₂ in L1544 decreases radially (Fig. 2), this raises the question of whether CRs levels also vary radially. The column densities of C₂S and C₃S exhibit significant radial variation and are moderately sensitive to changes in the cosmic-ray ionization rate, making them valuable probes for studying CRs. However, the chemical network for sulfur-bearing species remains incomplete. To address this limitation, we plan to use higher spatial resolution observations in conjunction with astrochemical modeling to explore the chemistry of sulfur-containing molecules across diverse interstellar environments.

5. Conclusion. In this work, we present observations of C₂S and C₃S in L1544 using the NSRT-26 m telescope and perform one-dimensional astrochemical modeling of these species to investigate the effects of the C/O ratio and cosmic-ray ionization rate on their formation pathways. Assuming LTE conditions, the calculated column densities for C₂S and C₃S were (4.4±0.6) × 10¹² and (8.7 ± 1.6) × 10¹¹, respectively. A comparison of the modeled column densities with the observationally derived values indicates that C₂S and C₃S likely originate from the outer layers of the core. We analyzed the impact of the C/O ratio and cosmic-ray ionization rate on the column densities of these molecules. Our findings reveal that while the column densities of C₂S and C₃S are relatively insensitive to variations within the chosen range of C/O ratios in L1544, they exhibit sensitivity to changes in the cosmic-ray ionization rate at specific locations. Consequently, C₂S and C₃S, alongside other molecular species, could serve as effective probes for measuring cosmic-ray ionization rates.

The characterization of CRs remains an active area of research in astrophysics, with robust constraints on cosmic-ray ionization in astrophysical contexts still being scarce. In recent years, China’s Five-hundred-meter Aperture Spherical Radio Telescope (FAST) has achieved significant advancements in various fields of astronomy. L1544, a prototypical prestellar core transitioning from the starless to protostellar phase, has been studied using FAST. Reference [41] reported the detection of magnetic field in L1544 with FAST. According to Ref. [42], the cold HI gas traced by HI narrow line self-absorption (HINSA) within molecular clouds can only be explained by cosmic-ray dissociation. FAST provides a unique opportunity to probe HINSA.^[43] Additionally, the FAST Core Array project plans to integrate FAST instruments into synthetic-aperture arrays,^[44] which is expected to enhance molecular detection capabilities. Combined observations with FAST and astrochemical modeling will contribute to a deeper understanding of the interactions between CRs and the interstellar medium.

Acknowledgements: X.H.L. acknowledges the support from the Natural Science Foundation of Xinjiang Uygur Autonomous Region (Grant No. 2024D01E37) and the National Science Foundation of China (Grant No. 12473025). This study was funded by the National Natural Science Foundation of China (Grant Nos. 12373026, 12203091, 12173075, and 11973076). WI, JG, and GF would like to thank the Xinjiang Tianchi Talent Program (2024). Tao Yang is grateful for the support from the Xinjiang Tianchi Talent Program (2023) and the Shanghai Natural Science Foundation (Grant No. 22ZR1421400). Xia Zhang thanks the Natural Science Foundation of Xinjiang Uygur Autonomous Region (Grant No. 2022D01A156). It was also partially funded by the Regional Collaborative Innovation Project of Xin jiang Uyghur Autonomous Region (Grant No. 2022E01050). We thank the assistance of the NSRT operators during the observations. The Nanshan 26 m Radio Telescope was partly supported by the Operation, Maintenance, and Upgrading Fund for Astronomical Telescopes and Facility Instruments funded by the Ministry of Finance of China and administered by the Chinese Academy of Sciences.

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Chemistry of C₂S and C₃S in L1544 with NSRT