Table 1: Description of the IRAM 30 m observations.
Line Freq. (GHz) HPBW $\eta_{\rm MB}$ Observed positions

N₂H⁺ 1 $\rightarrow$ 0 93 173.2 26.5'' 0.71 $60'' \times60 ''$ map

CN 1 $\rightarrow$ 0 113 490.0 23'' 0.65 $60'' \times60 ''$ map (FIRS 2), 60" $\times$ 100'' map (LkH $\alpha$ 234)

HCN 1 $\rightarrow$ 0 88 631.8 27.5'' 0.73 $60'' \times60 ''$ map (FIRS 2), 60" $\times$ 100'' map (LkH $\alpha$ 234)

H¹³CO⁺ 1 $\rightarrow$ 0 86 754.3 27.5'' 0.73 complete map

HC¹⁸O⁺ 1 $\rightarrow$ 0 85 162.2 27.5'' 0.73 (0, 0)

SiO 2 $\rightarrow$ 1 86 846.9 27.5'' 0.73 complete map

SiO 3 $\rightarrow$ 2 130 268.6 20'' 0.60 complete map

CS 3 $\rightarrow$ 2 146 969.0 16.5'' 0.55 complete map

C³⁴S 2 $\rightarrow$ 1 96 412.9 25.9'' 0.70 (0, 0)

C³⁴S 3 $\rightarrow$ 2 144 617.1 17'' 0.55 (0, 0)

C³⁴S 5 $\rightarrow$ 4 192 818.5 13'' 0.47 (0, 0)

CH₃OH 2(1, 3) $\rightarrow$ 1(1, 3) 96 755.5 26'' 0.70 72'' $\times$ 72'' map

CH₃OH 2(0, 3) $\rightarrow$ 1(0, 3) 96 744.6 26'' 0.70 72'' $\times$ 72'' map

CH₃OH 2(1, 4) $\rightarrow$ 1(1, 4) 96 741.4 26'' 0.70 72'' $\times$ 72'' map

CH₃OH 2(0, 1) $\rightarrow$ 1(0, 1) 96 739.4 26'' 0.70 72'' $\times$ 72'' map

CH₃OH 3(0, 3) $\rightarrow$ 2(0, 3) 145 093.7 17'' 0.55 (0, 0)

CH₃OH 3(1, 4) $\rightarrow$ 2(1, 4) 145 097.5 17'' 0.55 (0, 0)

CH₃OH 3(0, 1) $\rightarrow$ 2(0, 1) 145 103.2 17'' 0.55 (0, 0)

CH₃OH 3(2, 2) $\rightarrow$ 2(2, 2)^a 145 124.4 17'' 0.55 (0, 0)

CH₃OH 3(1, 3) $\rightarrow$ 2(1, 3) 145 131.9 17'' 0.55 (0, 0)

CH₃OH 5(2, 4) $\rightarrow$ 4(2, 4) 241 904.1 10'' 0.40 72'' $\times$ 72'' map

CH₃OH 5(0, 1) $\rightarrow$ 4(0, 1) 241 791.4 10'' 0.40 72'' $\times$ 72'' map

CH₃OH 5(1, 4) $\rightarrow$ 4(1, 4) 241 767.2 10'' 0.40 72'' $\times$ 72'' map

CH₃OH 5(3, 1) $\rightarrow$ 4(3, 1) 241 832.9^a 10'' 0.40 72'' $\times$ 72'' map

CH₃OH 5(2, 2) $\rightarrow$ 4(2, 2) 241 842.3 10'' 0.40 72'' $\times$ 72'' map

CH₃OH 8(1, 4) $\rightarrow$ 7(0, 3) 229 758.7 10.5'' 0.42 (0, 0)

CH₃OH 11(1, 4) $\rightarrow$ 10(2, 4) 104 300.5 24.5'' 0.68 (0, 0)

H₂CO 3₁₂ $\rightarrow$ 2₁₁ 225 697.8 10.5'' 0.43 60'' $\times$ 60'' map (FIRS 2), 72'' $\times$ 72'' map (LkH $\alpha$ 234)

H₂CO 2₁₂ $\rightarrow$ 1₁₁ 140 839.5 18'' 0.57 60'' $\times$ 60'' map (FIRS 2), 72'' $\times$ 72'' map (LkH $\alpha$ 234)

H₂¹³CO 2₁₂ $\rightarrow$ 1₁₁ 137 449.9 18'' 0.57 (0, 0)

CH₃CN 5(0) $\rightarrow$ 4(0) 91 987.0 27'' 0.72 (0, 0)

CH₃CN 5(1) $\rightarrow$ 4(1) 91 985.3 27'' 0.72 (0, 0)

CH₃CN 5(2) $\rightarrow$ 4(2) 91 980.0 27'' 0.72 (0, 0)

CH₃CN 5(3) $\rightarrow$ 4(3) 91 971.4 27'' 0.72 (0, 0)

CN 2 $\rightarrow$ 1 226 874.7 11'' 0.42 60'' $\times$ 60'' map (FIRS 2), $60'' \times 100 ''$ (LkH $\alpha$ 234)

N₂D⁺ 3 $\rightarrow$ 2 231 321.7 10.5'' 0.42 (0, 0)

DCO⁺ 2 $\rightarrow$ 1 144 077.3 17'' 0.56 60'' $\times$ 60'' map

DCO⁺ 3 $\rightarrow$ 2 216 112.6 11'' 0.44 60'' $\times$ 60'' map

D₂CO 4₀₄ $\rightarrow$ 3₀₃ 231 410.3 10.5'' 0.42 (0, 0)

^a Only observed with a frequency resolution of 1 MHz.

**Table 1:** Description of the IRAM 30 m observations.
Line	Freq. (GHz)	HPBW	$\eta_{\rm MB}$	Observed positions
N₂H⁺ 1 $\rightarrow$ 0	93 173.2	26.5''	0.71	$60'' \times60 ''$ map
CN 1 $\rightarrow$ 0	113 490.0	23''	0.65	$60'' \times60 ''$ map (FIRS 2), 60" $\times$ 100'' map (LkH $\alpha$ 234)
HCN 1 $\rightarrow$ 0	88 631.8	27.5''	0.73	$60'' \times60 ''$ map (FIRS 2), 60" $\times$ 100'' map (LkH $\alpha$ 234)
H¹³CO⁺ 1 $\rightarrow$ 0	86 754.3	27.5''	0.73	complete map
HC¹⁸O⁺ 1 $\rightarrow$ 0	85 162.2	27.5''	0.73	(0, 0)
SiO 2 $\rightarrow$ 1	86 846.9	27.5''	0.73	complete map
SiO 3 $\rightarrow$ 2	130 268.6	20''	0.60	complete map
CS 3 $\rightarrow$ 2	146 969.0	16.5''	0.55	complete map
C³⁴S 2 $\rightarrow$ 1	96 412.9	25.9''	0.70	(0, 0)
C³⁴S 3 $\rightarrow$ 2	144 617.1	17''	0.55	(0, 0)
C³⁴S 5 $\rightarrow$ 4	192 818.5	13''	0.47	(0, 0)
CH₃OH 2(1, 3) $\rightarrow$ 1(1, 3)	96 755.5	26''	0.70	72'' $\times$ 72'' map
CH₃OH 2(0, 3) $\rightarrow$ 1(0, 3)	96 744.6	26''	0.70	72'' $\times$ 72'' map
CH₃OH 2(1, 4) $\rightarrow$ 1(1, 4)	96 741.4	26''	0.70	72'' $\times$ 72'' map
CH₃OH 2(0, 1) $\rightarrow$ 1(0, 1)	96 739.4	26''	0.70	72'' $\times$ 72'' map
CH₃OH 3(0, 3) $\rightarrow$ 2(0, 3)	145 093.7	17''	0.55	(0, 0)
CH₃OH 3(1, 4) $\rightarrow$ 2(1, 4)	145 097.5	17''	0.55	(0, 0)
CH₃OH 3(0, 1) $\rightarrow$ 2(0, 1)	145 103.2	17''	0.55	(0, 0)
CH₃OH 3(2, 2) $\rightarrow$ 2(2, 2)^a	145 124.4	17''	0.55	(0, 0)
CH₃OH 3(1, 3) $\rightarrow$ 2(1, 3)	145 131.9	17''	0.55	(0, 0)
CH₃OH 5(2, 4) $\rightarrow$ 4(2, 4)	241 904.1	10''	0.40	72'' $\times$ 72'' map
CH₃OH 5(0, 1) $\rightarrow$ 4(0, 1)	241 791.4	10''	0.40	72'' $\times$ 72'' map
CH₃OH 5(1, 4) $\rightarrow$ 4(1, 4)	241 767.2	10''	0.40	72'' $\times$ 72'' map
CH₃OH 5(3, 1) $\rightarrow$ 4(3, 1)	241 832.9^a	10''	0.40	72'' $\times$ 72'' map
CH₃OH 5(2, 2) $\rightarrow$ 4(2, 2)	241 842.3	10''	0.40	72'' $\times$ 72'' map
CH₃OH 8(1, 4) $\rightarrow$ 7(0, 3)	229 758.7	10.5''	0.42	(0, 0)
CH₃OH 11(1, 4) $\rightarrow$ 10(2, 4)	104 300.5	24.5''	0.68	(0, 0)
H₂CO 3₁₂ $\rightarrow$ 2₁₁	225 697.8	10.5''	0.43	60'' $\times$ 60'' map (FIRS 2), 72'' $\times$ 72'' map (LkH $\alpha$ 234)
H₂CO 2₁₂ $\rightarrow$ 1₁₁	140 839.5	18''	0.57	60'' $\times$ 60'' map (FIRS 2), 72'' $\times$ 72'' map (LkH $\alpha$ 234)
H₂¹³CO 2₁₂ $\rightarrow$ 1₁₁	137 449.9	18''	0.57	(0, 0)
CH₃CN 5(0) $\rightarrow$ 4(0)	91 987.0	27''	0.72	(0, 0)
CH₃CN 5(1) $\rightarrow$ 4(1)	91 985.3	27''	0.72	(0, 0)
CH₃CN 5(2) $\rightarrow$ 4(2)	91 980.0	27''	0.72	(0, 0)
CH₃CN 5(3) $\rightarrow$ 4(3)	91 971.4	27''	0.72	(0, 0)
CN 2 $\rightarrow$ 1	226 874.7	11''	0.42	60'' $\times$ 60'' map (FIRS 2), $60'' \times 100 ''$ (LkH $\alpha$ 234)
N₂D⁺ 3 $\rightarrow$ 2	231 321.7	10.5''	0.42	(0, 0)
DCO⁺ 2 $\rightarrow$ 1	144 077.3	17''	0.56	60'' $\times$ 60'' map
DCO⁺ 3 $\rightarrow$ 2	216 112.6	11''	0.44	60'' $\times$ 60'' map
D₂CO 4₀₄ $\rightarrow$ 3₀₃	231 410.3	10.5''	0.42	(0, 0)

Source LaTeX | All tables | In the text

	1 Introduction
	2 Target selection and observational strategy
	3 Observations
	4 Analysis
	5 Results
	6 Deuterated compounds
	7 Discussion
	8 Summary and conclusions: Chemical clocks in intermediate-mass YSOs
	References
	Online Material