Interstellar HOC$^{+}$ Revisited

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Session 81 -- YSO's, Masers and Molecules
Display presentation, Wednesday, 11, 1995, 9:20am - 6:30pm

[81.11] Interstellar HOC$^{+}$ Revisited

A.J.Apponi, L.M.Ziurys (ASU)

One abundance ratio of importance for astrochemistry is [HCO$^{+}$] / [HOC$^{+}$]. HOC$^{+}$ is the metastable isomer of HCO$^{+}$ and lies about 17,000 K higher in energy. Both theory and experiment suggest that this ratio should be $>$ 10$^{4}$ in interstellar gas. A tentative detection of the J=1-0 transition of HOC$^{+}$ towards SgrB2(OH) by Woods et al.(Ap.J.370 , 538), however, indicates that [HCO$^{+}$]/[HOC$^{+}$]$\sim$330. We report here on new observations to confirm the identification of interstellar HOC$^{+}$ and establish the true [HCO$^{+}$]/[HOC$^{+}$] ratio. We have detected spectral lines at the frequency of the J=1-0 transition of HOC$^{+}$ at 89 GHz towards several new sources, including Orion-KL, W51, and DR21(OH), using the NRAO 12 m telescope. In addition, we have observed lines at the J=3-2 frequency of this molecular ion at 268 GHz in SgrB2(OH) and Orion-KL. These measurements suggest that the [HCO$^{+}$]/[HOC$^{+}$] ratio established by Woods et al. may be correct, and that HOC$^{+}$ is more abundant than chemical models predict.

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