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Handbook of Frequency Allocations and Spectrum Protection for Scientific Uses: Second Edition (2015)

Chapter: Appendix C: International Astronomical Union Spectral Lines of Most Importance Below 300 GHz

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Suggested Citation: "Appendix C: International Astronomical Union Spectral Lines of Most Importance Below 300 GHz." National Academies of Sciences, Engineering, and Medicine. 2015. Handbook of Frequency Allocations and Spectrum Protection for Scientific Uses: Second Edition. Washington, DC: The National Academies Press. doi: 10.17226/21774.

C

International Astronomical Union Spectral Lines of Most Importance Below 300 GHz

At each triennial meeting of the General Assembly, the International Astronomical Union (IAU) reviews carefully the list of astrophysically most important spectral lines that it maintains. The IAU expresses the need to protect these frequency bands from in-band, band-edge, and harmonic emissions, especially from spaceborne transmitters.

In preparation for World Radiocommunication Conference 2000, which revised the allocations above 71 GHz, a millimeter-wavelength working group of the Scientific Committee on Frequency Allocations for Radio Astronomy and Space Science (IUCAF) examined all then-known transitions in the millimeter and submillimeter wavebands. The working group selected a limited number of the astrophysically most important spectral lines to supplement the earlier lists, such as those produced by the IAU, to be used in allocating frequency bands to the Radio Astronomy Service. Spectral lines below 300 GHz are listed in Table C.1. Unless otherwise noted, the suggested minimum band limits are Doppler-shifted frequencies corresponding to radial velocities of ±300 km/s, consistent with line radiation occurring in our Milky Way galaxy. Spectral lines with primary (P), secondary (S), or footnote (F) protection status are noted in Table C.1.

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TABLE C.1 The Most Important Spectral Lines Below 300 GHz


Species	Formula	Frequency (GHz)	Suggested Minimum Band (GHz)	Band Allocation Status	Notes (1)

Deuterium	Di	0.327384	0.327-0.3277	P
Hydrogen	Hi	1.420406	1.370-1.427	S 1.33-1.40	2, 3
Hydrogen	Hi	1.420406	1.370-1.427	P 1.40-1.427	2, 3
Hydroxyl radical	OH	1.612231	1.6068-1.6138	P 1.6106-1.6138	4
		1.665402	1.6598-1.6671	P 1.66-1.67	4
		1.667359	1.6618-1.6690		4
Hydroxyl radical	OH	1.720530	1.7148-1.7222	S 1.7188-1.7222	3, 4
Methyladyne	CH	3.263794	3.2424-3.2671	S 3.260-3.267	3, 4
		3.335481	3.3244-3.3388	S 3.332-3.339	3, 4
		3.349193	3.3380-3.3525	S 3.3458-3.3525	3, 4
Formaldehyde	H₂CO	4.829660	4.8136-4.8345	S 4.8-4.9	3, 4
Methanol	CH₃OH	6.668518	6.6618-6.6752	S 6.650-6.6752	3
Helium	³He⁺	8.665650	8.6570-8.6743		3, 6
Methanol	CH₃OH	12.178	12.17-12.19		3, 6
Formaldehyde	H₂CO	14.488	14.44-14.50	S 14.47-14.50	3, 4
Cyclopropenylidene	C₃H₂	18.343	18.28-18.36		3, 4, 6
Water vapor	H₂O	22.235	22.16-22.26	F 22.01-22.21	3, 4
Water vapor				P 22.21-22.50
Ammonia	NH₃	23.694	23.61-23.71	P 23.60-24.00	4
		23.723	23.64-23.74		4
		23.870	23.79-23.89		4
Sulphur monoxide	SO	30.002	29.97-30.03		6
Methanol	CH₃OH	36.169	36.13-36.21	P 36-37	6
Silicon monoxide	SiO	42.519	42.47-42.57	F 42.77-42.87	6, 8
		42.821	42.78-42.86	F 43.07-43.17
		43.122	43.08-43.17	F 43.37-43.47
		43.424	43.38-43.47
Dicarbon monosulphide	CCS	45.379	45.33-45.42		6
Carbon monosulphide	CS	48.991	48.94-49.04	P 48.94-49.04
Oxygen	O₂	61.1	56.21-63.06	P 58.2-59.0	5, 6, 7
Deuterated water	HDO	80.578	80.50-80.66
Cyclopropenylidene	C₃H₂	85.339	85.05-85.42
Silicon monoxide	SiO	86.243	86.16-86.33	P
Formylium	H¹³CO⁺	86.754	86.67-86.84	P
Silicon monoxide	SiO	86.847	86.76-86.93	P
Ethynyl radical	C₂H	87.300	87.21-87.39	P	5
Hydrogen cyanide	HCN	88.632	88.34-88.72	P	4
Formylium	HCO⁺⁺	89.189	88.89-89.28	P	4
Hydrogen isocyanide	HNC	90.664	90.57-90.75	P

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Species	Formula	Frequency (GHz)	Suggested Minimum Band (GHz)	Band Allocation Status	Notes (1)

Diazenylium	N₂H⁺	93.174	93.08-93.27
Carbon monosulphide	CS	97.981	97.65-98.08		4
Sulfur monoxide	SO	99.300	99.20-99.40
Methyl acetylene	CH₃CCH	102.5	102.39-102.60		5
Methanol	CH₃OH	107.014	106.91-107.12
Carbon monoxide	C¹⁸O	109.782	109.67-109.89	P
Carbon monoxide	¹³CO	110.201	110.83-110.31	P	4
Carbon monoxide	C¹⁷O	112.359	112.25-112.47	P	6
Cyano radical	CN	113.500	113.39-113.61	P	5
Carbon monoxide	CO	115.271	114.88-115.39	P	4
Oxygen	O₂	118.750	118.63-118.87	P 116-126	7
Formaldehyde	H₂¹³CO	137.450	137.31-137.59		6
Formaldehyde	H₂CO	140.840	140.69-140.98	P
Carbon monosulphide	CS	146.969	146.48-147.12	P 146.82-147.12
Nitric oxide	NO	150.4	149.95-150.85	S 150-151	5
Methanol	CH₃OH	156.602	156.45-156.76
Water vapor	H₂O	183.310	183.13-183.49
Carbon monoxide	C¹⁸O	219.560	219.34-219.78	P
Carbon monoxide	¹³CO	220.399	219.67-220.62	P	4
Cyano radical	CN	226.600	226.37-226.83	P	5
Cyano radical	CN	226.800	226.57-227.03	P	5
Carbon monoxide	CO	230.538	229.77-230.77	P	4
Carbon monosulphide	CS	244.953	244.14-245.20		6
Nitric oxide	NO	250.6	250.35-250.85	P	5
Ethynyl radical	C₂H	262.000	261.74-262.26		5
Hydrogen cyanide	HCN	265.886	265.00-266.15
Formylium	HCO⁺⁺	267.557	266.66-267.82
Hydrogen isocyanide	HNC	271.981	271.71-272.25
Diazenylium	N₂H⁺	279.511	279.23-279.79
Carbon monosulphide	CS	293.912	292.93-294.21

NOTES:

1. If Notes 2 or 4 are not listed, then the band limits are the Doppler-shifted frequencies corresponding to radial velocities of ± 300 km/s (consistent with line radiation occurring in our Milky Way galaxy).

2. An extension to lower frequency of the allocation of 1 400-1 427 MHz is required to allow for the higher Doppler shifts for HI observed in distant galaxies.

3. The current international allocation is not primary and/or does not meet bandwidth requirements. See the Radio Regulations (RR) for more detailed information.

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4. Because these line frequencies are also being used for observing other galaxies, the listed bandwidths include Doppler shifts corresponding to radial velocities of up to 1,000 km/s. It should be noted that HI has been observed at frequencies redshifted to 500 MHz, while some lines of the most abundant molecules have been detected in galaxies with velocities up to 50,000 km/s, corresponding to a frequency reduction of up to 17%.

5. There are several closely spaced lines associated with these molecules. The listed bands are wide enough to permit observations of all lines.

6. This line frequency is not mentioned in RR Article 5.

7. These lines are observable only outside the atmosphere.

8. A portion of the “suggested minimum band” for this line extends outside the band allocated to the radio astronomy service. Protection for observations conducted in this portion of the band may not be practicable.

SOURCE: Data and further information can be found in the International Telecommunication Union, RA 314 Series: Preferred Frequency Bands for Radio Astronomical Measurements, June 2003, http://www.itu.int/dms_pubrec/itu-r/rec/ra/R-REC-RA.314-10-200306-I!!PDF-E.pdf.

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Next Chapter: Appendix D: International Astronomical Union Spectral Lines of Most Importance Between 300 and 1000 GHz

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Handbook of Frequency Allocations and Spectrum Protection for Scientific Uses: Second Edition (2015)

Chapter: Appendix C: International Astronomical Union Spectral Lines of Most Importance Below 300 GHz