The ketenyl radical is almost linear with the
Ka = 1 levels being so high in energy that
for astronomical observations it can be treated as being linear.
M. Agúndez, J. Cernicharo, and M. Guélin
reported on the
Discovery of Interstellar Ketenyl (HCCO), a Surprisingly Abundant Radical
Astron. Astrophys. 577, Art. No. L5 (2015).
The IRAM 30 m telescope was used to detect the four ΔF = ΔJ = ΔN hyperfine components with N = 4 3 near 86.65 GHz toward two peculiar dark clouds Lupus-1A and L483.