PDRs4All - IV. An embarrassment of riches: Aromatic infrared bands in the Orion Bar

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Volume 685 (May 2024)

A&A, 685 (2024) A75

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Table A.1

Catalogue of AIB features detected in the five template spectra of the Orion Bar. The method used to select these features is described in Sect. 3. The precise peak positions of nominal AIBs – whose wavelengths appear in boldface in this table – are indicated in Col. 3. We note that we converted the positions in wavelength to wavenumber by rounding to the nearest integer in units of cm⁻¹, and so the precision of the reported wavenumbers do not reflect the precision of the peak position of the AIBs.

AIB		Components		New? (5)	I_peak	Characteristics	Assignment
µm (1)	cm⁻¹ (2)	µm (3)	cm⁻¹ (4)		(6)	(7)	(8)
3 µm (3000 cm⁻¹) region^a
3.3	3030				vs		(aromatic) CH stretches
		3.246	3081		ms	symm, blend
		3.290	3040		vs	symm, blend
3.4	2941				s, ms	asymm, blend	CH stretches in aliphatic groups (methyl (CH3) and ethyl (CH2CH3) groups attached to PAHs and superhy-drogenated PAHs)
		3.395	2946		s, ms	blend
		3.403	2939		s, ms	blend
		3.424	2921	✓	ms, mw	blend
3.465	2886				ms, mw	symm, blend	CH stretches in aliphatic groups (see 3.4 µm AIB)
3.516	2844				ms, mw	symm, blend	CH stretches in aliphatic groups (see 3.4 µm AIB)
3.561	2808				mw, w	symm, blend	CH stretches in aliphatic groups (see 3.4 µm AIB)

5–6 µm(1600–2000 cm⁻¹) range
5.25	1905				mw	asymm	combination bands generated by modes of the same type, e.g., out-of-plane (OOP) modes
		~5.18	~1931		w, vw	blue shoulder
		5.236	1910		mw	asymm
		~5.30	~1887	✓	vw^b	blend
5.435?	1840?			✓	vw	symm?, often blend (5.25)	combination bands (see 5.25 µm AIB)
5.535?	1807?			✓	vw	symm?, blend (5.75)	combination bands (see 5.25 µm AIB)
5.75	1739				mw		combination bands (see 5.25 µm AIB)
		5.642	1772	✓	mw	blend, symm
		5.699	1755	✓	mw	blend, symm
		5.755	1738	✓	mw	blend, symm
5.878	1701			✓	mw, w	blend (5.75), symm	combination bands (see 5.25 \| m AIB)

6.2 µm (1610 cm⁻¹) AIB
6.024	1660				w, vw^b	blend (6.2), symm	C=O stretch in conjugated carbonyl groups i.e., as quinones or attached to aromatic rings
6.2	1613				vs	asymm	pure aromatic CC stretching mode
		~6.07	~1647	✓	mw	blue shoulder
		6.212	1610		vs	asymm
		~6.395	~1564	✓?	vw^b	blend
		~6.50?	~1538?	✓?	vw	slope change

7.7 µm (1300 cm⁻¹) AIB complex
6.638	1506				vw	blend (6.711), symm	modes with a mixed character of CC stretching and CH in-plane bending
6.711	1490			✓?	vw	blend (6.638), symm	see 6.638 µm AIB
6.850	1460				vw	blend (6.943), symm	CH deformation mode of aliphatic groups
6.943	1440				vw	blend (6.850), symm	CH deformation mode of aliphatic groups
7.7	1299				vs		see 6.638 µm AIB
		~7.05?	~1418?	✓	vw^b	slope change
		~7.10	~1408	✓	vw^b	slope change
		~7.24	~1381		vw^b	blend
		~7.43	~1346		vw^b	slope change
		~7.626	~1311		vs	blend
		7.8	1290
		↳ ~7.743	↳ ~1291	✓	ms^b	blend
		↳ ~7.775	↳ ~1286	✓	ms^b	blend
		~7.85	~1274	✓	ms^b	blend
8.223	1216			✓?	vw^b	blend	see 6.635 µm AIB
8.330	1200				vw, w^b	blend, symm	see 6.635 µm AIB

8.6 µm (1160 cm⁻¹) AIB complex
8.6	1163				s	symm	CH in-plane bending with large CC stretching admixture
		~8.46	~1182	✓	vw^b	slope change
		~8.54	~1171	✓	vw^b	slope change
		8.60	1163		S	symm
		~8.74?	~1144?	✓	vw^b	slope change
		~8.89?	~1125?	✓	w, vw^b	slope change

10–20 µm (500–1000 cm⁻¹) range^c
~10.95	~913				w	blue shoulder	solo CH out-of-plane bending
11.005	909				mw, w^b	blend (11.2), symm	solo CH out-of-plane bending
11.2	893				vs	asymm	solo CH out-of-plane bending
		~11.207	~892		vs	blend
		~11.25	~889	✓	ms^b	blend
		~11.275?	~887?	✓	mw^b	blend
12.0^d	833^d				ms, mw	blend (11.2)	duo CH out-of-plane bending
		11.955	836		mw, w^b
		12.125?^d	825?^d	✓	W^b	slope change
12.7^d	787^d				S, ms	asymm	duo, trio CH out-of-plane bending
		~12.38	~808	✓	mw^b	blend
		~12.52?	~799?		mw^b	blend
		~12.625	~792	✓	mw^b	blend
		12.729	786	✓	s, ms	blend
		12.779	783	✓	s, ms	blend
		~12.98	~770	✓	W^b	red shoulder
13.5^d	741^d				mw, w		quartet CH out-of-plane bending
		~13.50?	~738?	✓	w, vw^b	blend
		13.55			mw,w	peak
		~13.62	~734	✓	vw^b	blend
13.95?^d	717?^d				w, vw^b		quintet CH out-of-plane bending, CCC skeletal
14.21^d	704^d				mw, w^b		quintet CH out-of-plane bending, CCC skeletal
16.43	609				ms	asymm	CCC skeletal

Notes. Columns: (1) Wavelength of AIB; nominal AIB names are listed in boldface; (2) Wavenumber of AIB; (3) Wavelength of component; (4) Wavenumber of component; (1)-(4) Tentative detection indicated by ‘?’; (5) New detection; (6) Peak intensity relative to the 3.3, 7.7 or 11.2 peak intensity for bands in the 3–4, 5–10, and 10–15 range, respectively. The categories are vs (> 65%), s (> 35%), ms (> 15%), mw (> 5%), w (> 2%), and vw (< 2%), where v=very, m=moderate, s=strong, and w=weak. The relative peak intensity of AIBs strongly depend on the employed continuum and spectral decomposition; (7) symmetric profile (symm); asymmetric profile (asymm); blended with another band/component at x (blend (x)); change of slope (slope change); (8) vibrational assignment. ^(a)From Peeters et al. (2023). ^(b)Estimated assuming the component is superimposed on other AIB component(s) such as, e.g., a blue or red wing or shoulder, i.e. we assume a local continuum. ^(c)We only list the strongest band in the 15-20 region as it suffers from calibration issues (Appendix B). ^(d)Influenced by artefact(s) (Appendix B).

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