, M. Guélin 
Observatorio Astronomico Nacional, apartado 1143,
E--28800 Alcalá de Henares, Spain
IRAM, 300 Rue de la piscine, F--38406 S
Martin
d'Hères, France 
H and C
H in the carbon star envelope IRC+10216, we have
identified 10 lines with harmonically related frequencies and with regularly
increasing intensities (3 lines in the IRAM 3 mm spectral survey and 7 lines in
the 7 mm Nobeyama survey of Kawaguchi et al., 1995). The rest frequencies can
be closely fitted with the standard expression for the energies of a linear
molecule with a rotational constant 
MHz, a distortion constant 
Hz, and half-integer quantum numbers J. The value of B is within 0.1%
of that predicted by Pauzat et al. (1991) for the 
ground state of
C
H and the value of D typical of a linear acetylenic chain of C
H's
weight. Since the half-integer J numbers are also consistent with a 
state, we concluded that we had very probably discovered C
H.
The non detection of 
-doubling, as well as of a second
series of lines corresponding to the other fine structure state,
suggested that the C
H ground state is inverted and that we
were observing the 
state.
Our identification is now confirmed in the laboratory: M. Carthy et al. (1996)
succeeded in detecting 30 millimeter lines arising from the new radical in an acetylene
discharge and confirmed that their carrier is indeed C
H.
The rotation temperature diagram of the C
H lines observed
in IRC+10216 is shown in Fig. 1. The fitted
straight line yields a rotation temperature 
= 52 K and
a beam-averaged column density 
cm
. This latter is a factor of 30 lower than the column
density of C
H; it is similar to the column density predicted by
Millar & Herbst (1991) in the case of a medium-large acetylene
abundance ([H
C
]/[H
]= 2.5 10
)
We found no trace of C
H in either the 30-m telescope, or the 45-m telescope
data.
Figure 3: The rotational temperature diagram of the 10 lines assigned to C
H.
Typical errors on the line integrated intensities W are 20%.
References:
