Deuterium fractionation and the degree of ionisation in massive clumps within infrared dark clouds

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Volume 534 (October 2011)

A&A, 534 (2011) A134

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Table 2

Observed spectral-line transitions and observational parameters.

Transition	ν	E_u/k_B	n_crit	HPBW	η_MB	T_sys	Channel spacing^a		t_int
	[MHz]	[K]	[10⁶ cm^-3]	[″]		[K]	[kHz]	[km s^-1]	[min]

DCO⁺(3−2)	216 112.57790^b	20.7	1.8	28.9	0.75	150–184	122.07	0.17	5.5–13.5
C¹⁷O(2−1)	224 714.199^c	16.2	0.01	27.8	0.75	163–218	61.04^d	0.08^d	5–7.5
N₂D⁺(3−2)	231 321.912^e	22.2	1.7	27.0	0.75	172–239	122.07	0.16	6.5–48
H¹³CO⁺(3−2)	260 255.35250^b	25.0	3.1	24.0	0.74	232–243	122.07	0.14	2.5–27
N₂H⁺(3−2)	279 511.832^e	26.8	3.0	22.3	0.74	165–175	122.07	0.13	1.5–6.5

Notes. Columns (2)–(4) give the rest frequencies of the observed transitions (ν), their upper state energies (E_u/k_B, where k_B is the Boltzmann constant), and critical densities. Critical densities were calculated at T ~ 15 K (typical value in IRDCs) using the collisional rate data available in the Leiden Atomic and Molecular Database (LAMDA; http://www.strw.leidenuniv.nl/~moldata/) (Schöier et al. 2005). For N₂D⁺, we used the Einstein A-coefficient from Pagani et al. (2009b) and the same collisional rate as for N₂H⁺. Columns (5)–(10) give the APEX beamsize (HPBW) and the main beam efficiency (η_MB) at the observed frequencies, and the SSB system temperatures during the observations (T_sys in scale, see text), channel widths (both in kHz and km s^-1) of the original data, and the on-source integration times per position (t_int).

^(a)

The original channel spacings. The final spectra were Hanning-smoothed, which divides the number of channels by two.

^(b)

From the CDMS spectroscopic database (Müller et al. 2005).

^(c)

From Ladd et al. (1998).

^(d)

For the C¹⁷O(2−1) observations towards J18364 SMM1, channel width is 122.07 kHz or 0.16 km s^-1.

^(e)

From Pagani et al. (2009b).

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