Chemical evolution in the early phases of massive star formation. I

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Table 2

List of analyzed molecules with transitions, frequencies, energies of the upper level, critical densities, and effective densities calculated for 10 K and 100 K^a.

Molecule	Transition	Frequency	E_u/k	n_crit for T = 10 K	n_crit for T = 100 K	n_eff for T = 10 K	n_eff for T = 100 K
		[GHz]	[K]	[10⁵cm^-3]	[10⁵cm^-3]	[10³cm^-3]	[10³cm^-3]

H¹³CO⁺	1−0	86.7543	4.2	1.5	2.1	3	0.9
SiO	2−1	86.8470	6.3	2.7	3.0	20	4
HN¹³C	1−0	87.0909	4.2		10^b	–	–
C₂H	1_3/2,2 − 0_1/2,1	87.3169	4.2		1^c	–	–
HNCO	4(0,4)–3(0,3)	87.9252	10.6	9.8^d	5.3^e	30	3
HCN	1−0	88.6316	4.3	10.1	26.6	29	5.1
CH₃OCHO	7(2,5)–6(2,4) E	90.1456	19.7		–	–	–
CH₃CN	5−4 (K = 2)	91.9800	41.8	4.2^d	2.7	–	20
¹³CS	2−1	92.4943	6.7	3.3^f	3.8^f	–	–
N₂H⁺	1−0	93.1737	4.5	1.4	2.0	4	2
H₂CO(para)^g	3(0,3)–2(0,2)	218.2221	21.0	23.5	50.3	100	15
CH₃OH^h	4(2,2)–3(1,2)	218.4401	45.5	133.9	781.1	–	–
H₂CO(para)ⁱ	3(2,2)–2(2,1)	218.4756	68.1	30.2	56.1	–	50
OCS^j	18–17	218.9034	99.8	4.2	4.0	–	–
C¹⁸O	2−1	219.5604	15.8	0.08	0.10	–	–
SO	6−5	219.9488	35.0	22.6^k	37.4	–	50
C³³S	5−4	242.9136	35.0	51.4^f	54.0^f	–	–
OCS^l	20–19	243.2180	122.6	5.9	5.6	–	–
CH₃OH^m	5(1,4)–4(1,3)	243.9158	49.7	8.0	15.5	–	–

Notes.

^(a)

Values are taken from the LAMDA database (Schöier et al. 2005), unless otherwise noted. Other species, visible in Fig. 1, were not analyzed due to presumed high optical depth, as explained in the text. The effective densities were calculated with RADEX (van der Tak et al. 2007) assuming (Evans 1999). For some molecules only the value for T = 100 K is given, because at T = 10 K the transition is too weak;

^(b)

Sakai et al. (2012);

^(c)

Sakai et al. (2010);

^(d)

For T = 20 K;

^(e)

For T = 80 K;

^(f)

Value for the main isotopologue C³⁴S;

^(g)

Hereafter referred to as H₂CO-K0;

^(h)

Hereafter referred to as CH₃OH-4;

⁽ⁱ⁾

Hereafter referred to as H₂CO-K2;

^(j)

Hereafter referred to as OCS-18;

^(k)

For T = 60 K;

^(l)

Hereafter referred to as OCS-20;

^(m)

Hereafter referred to as CH₃OH-5.

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