Figure: H12,C16,O , H13,CO
(
),
H12,C14,N, H13,C14,N (
), H14,N12,C, and
12,C32,S (J=2-1) absorption spectra toward B0415+379=3C111
(solid lines) with H12,C18,O
(
),
H12,C15,N (
), H14,N13,C (
) and
C34,S overlaid (shaded).
We have measured galactic mm absorption spectra of HCO
,
HCN, HNC, and CS toward compact extragalactic continuum sources in
order to derive the isotopic abundance ratios
C/
C,
N/
N,
O/
O,
and
S/
S in local diffuse clouds. For carbon, our data confirm
recent results for the local ISM: we find
C/
C =
. For
nitrogen, we find
consistent with the Solar
value of 270, but substantially smaller than the values inferred
from HCN emission in dense clouds. For sulfur we find
S/
S\
consistent with the Solar value of 23. We also find
one striking individual anomaly: toward 3C111 (B0415+379),
H12,CN/H13,CN = 170
in one kinematic component
(Fig. 3). We attribute this to the fractionation of
13,C into 13,CO which may be so great that HCN is starved
for 13,C.
Preprints:http://iram.fr/ lucas/papers/isotopes.ps.gz