We report detection of the 609 \mu m ^ { 3 } P _ { 1 } \rightarrow { { } ^ { 3 } P _ { 0 } } line of neutral atomic carbon in globules of the Helix nebula .
The measurements were made towards the position of peak CO emission .
At the same position , we obtained high-quality CO ( 2–1 ) and ^ { 13 } CO ( 2–1 ) spectra and a 135 \arcsec \times 135 \arcsec map in CO ( 2–1 ) .
The velocity distribution of C I shows six narrow ( 1–2 km s ^ { -1 } ) components which are associated with individual globules traced in CO .
The C I column densities are 0.5–1.2 \times 10 ^ { 16 } cm ^ { -2 } .
C I is found to be a factor of \sim 6 more abundant than CO .
The large abundance of C I in the Helix can be understood as a result of the gradual photoionisation of the molecular envelope by the central star ’ s radiation field .