September 2019

The pure carbon molecule C5 was detected toward IRC +10216 (CW Leo) by Bernath et al. in 1989 using the 4-meter telescope at Kitt Peak National Observatory. Since C5 has no dipole moment and thus no rotational spectrum, it was detected via a particularly intense vibrational mode (see below), which gives rise to a ro-vibrational spectrum that was used to detect the molecule. To date, C5 has only been detected in the one source. It has been unsuccessfully sought toward ζ Oph by Maier et al. and toward various translucent clouds by Galazutdinov et al.

Researcher Links
PF Bernath
KH Hinkle
KK Keady

No vibrational spectrum was available when Bernath et al. set out to search for C5. Vala et al. characterized it. A number of additional experimental studies have followed. For example, Heath et al. measured the ro-vibrational spectrum (and published back-to-back with the detection), Moazzen-Ahmadi et al. characterized the 13C spectroscopy of the intense band, and Boguslavskiy & Maier measured its electronic spectrum.

C5 or pentatetraenediylidene or, more precisely, 1,2,3,4-pentatetraene-1,5-diylidene, is related to other known astromolecules, particularly C3, C5H, and C5S. C5 is a classic carbene.

The vibrational mode used to detect C5 is known as the ν3 mode. It is far and away the most intense of the molecule's few active vibrational modes. It is an asymmetric stretch that looks like this.

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