Appendix 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) carefully reviews 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 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 band limits are Doppler-shifted frequencies corresponding to radial velocities of ± 300 km/s, consistent with line radiation occurring in the Galaxy. These data and further information can be found on the Web site of the European Science Foundation’s Committee on Radio Astronomy Frequencies at http://www.astron.nl/craf/iaulist.htm.)



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Handbook of Frequency Allocations and Spectrum Protection for Scientific Uses Appendix 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) carefully reviews 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 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 band limits are Doppler-shifted frequencies corresponding to radial velocities of ± 300 km/s, consistent with line radiation occurring in the Galaxy. These data and further information can be found on the Web site of the European Science Foundation’s Committee on Radio Astronomy Frequencies at http://www.astron.nl/craf/iaulist.htm.)

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Handbook of Frequency Allocations and Spectrum Protection for Scientific Uses TABLE C.1 The Most Important Spectral Lines Below 275 GHz Substance Formula Frequency (GHz) Suggested Minimum Band (GHz) Band Allocation Status1 Deuterium D I 0.327384 0.327-0.3277 P Hydrogen HI 1.4204062,3 1.370-1.427 S 1.33-1.40         P 1.40-1.427 Hydroxyl radical OH 1.6122314,5 1.6068-1.6138 P 1.6106-1.6138     1.6654026 1.6598-1.6671 P 1.66-1.67     1.6673596 1.6618-1.6690   Hydroxyl radical OH 1.7205303,6 1.7148-1.7222 S 1.7188-1.7222 Methyladyne CH 3.2637943,6 3.2424-3.2671 S 3.260-3.267     3.3354813,6 3.3244-3.3388 S 3.332-3.339     3.3491933,6 3.3380-3.3525 S 3.3458-3.3525 Formaldehyde H2CO 4.8296603,6 4.8136-4.8345 S 4.8-4.9 Methanol CH3OH 6.6685183,7 6.6618-6.6752 S 6.650-6.6752 Helium 3He+ 8.665650 8.6570-8.6743   Methanol CH3OH 12.1783,8 12.17-12.19   Formaldehyde H2CO 14.4883,6 14.44-14.50 S 14.47-14.50 Cyclopropenylidene C3H2 18.3433,6,8 18.28-18.36   Water vapor H2O 22.2353,6 22.16-22.26 F 22.01-22.21         P 22.21-22.50 Dicarbon monosulphide CCS 22.344 22.32-22.37   Ammonia NH3 23.6946 23.61-23.89 P 23.60-24.00     23.7236 23.8706   Sulphur monoxide SiO 30.002 29.97-30.03   Methanol CH3OH 36.169 36.13-36.21 P9 36-37 Silicon monoxide SiO 42.519 42.47-42.57       42.821 42.78-42.86 F 42.77-42.87     43.122 43.08-43.17 F 43.07-43.17     43.424 43.38-43.47 F 43.37-43.37 Dicarbon monosulphide CCS 45.379 45.33-45.42   Carbon monosulphide CS 48.991 48.94-49.04 P 48.94-49.04 Oxygen O2 61.1 56.21-63.06 P10 58.2-59.0 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 87.30011 87.21-87.39 P

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Handbook of Frequency Allocations and Spectrum Protection for Scientific Uses Substance Formula Frequency (GHz) Suggested Minimum Band (GHz) Band Allocation Status1 Hydrogen cyanide HCN 88.6326 88.34-88.72 P Formylium HCO++ 89.1896 88.89-89.28 P Hydrogen isocyanide HNC 90.664 90.57-90.75 P Diazenylium N2H+ 93.174 93.08-93.27   Carbon monosulphide CS 97.9816 97.65-98.08   Sulfur monoxide SO 99.300 99.20-99.40   Methyl acetylene CH3CCH 102.5 102.39-102.60   Methanol CH3OH 107.014 106.91-107.12   Carbon monoxide C18O 109.782 109.67-109.89 P Carbon monoxide 13CO 110.2016 110.83-110.31 P Carbon monoxide C17O 112.3598 112.25-112.47 P Cyano radical CN 113.500 113.39-113.61 P Carbon monoxide CO 115.2716 114.88-115.39 P Oxygen O2 118.750 118.63-118.87 P6 116-126 Formaldehyde H213CO 137.4503,8 137.31-137.59   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 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 220.3996 219.67-220.62 P Cyano radical CN 226.600 226.37-226.83 P Cyano radical CN 226.800 226.57-227.03 P Carbon monoxide CO 230.5386 229.77-230.77 P Carbon monosulphide CS 244.9538 244.14-245.20   Nitric oxide NO 250.6 250.35-250.85 P Ethynyl radical C2H 262.000 261.74-262.26   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   Carbon monosulphide 13CS 277.455 277.18-277.73   Diazenylium N2H+ 279.511 279.23-279.79   Carbon monosulphide C34S 289.209 288.92-289.50   Sodium hydride NaH 289.860 289.57-290.15   Carbon monosulphide CS 293.912 292.93-294.21  

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Handbook of Frequency Allocations and Spectrum Protection for Scientific Uses NOTE: Definitions of abbreviations for the various services referred to in the footnotes to this table are provided in Appendix I. 1P: primary allocation, S: secondary allocation, F: protection by footnote. 2An extension to lower frequencies of the allocation of 1400-1427 MHz is required to allow for the Doppler shifts for HI observed in distant galaxies. 3For passive EESS and SRS, along with FS and MS. 4The current international allocation is not primary and/or does not meet bandwidth requirements. See the ITU-R Radio Regulations for more detailed information. 5Because these line frequencies are also being used for observing other galaxies, the listed bandwidths include Doppler shifts corresponding to radial velocities of up to 1000 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%. 6For passive EESS and SRS, along with FS and MS. 7This line is not mentioned in Article 8 of the ITU-R Radio Regulations. 8For passive EESS and SRS, along with FS and MS. 9For passive EESS and SRS, with secondary allocations to FS and MS. 10United States only. 11There are six closely spaced lines associated with this molecule at this frequency. The listed band is wide enough to permit observations of all six lines. SOURCE: Data and further information can be found at the Web site of the European Science Foundation’s Committee on Radio Astronomy Frequencies at http://www.astron.nl/craf/iaulist.htm, accessed October 26, 2005.