SUBMILLIMETER OBSERVATION OF HCO$^+$ AND DCO$^+$ IN THE EXCITED VIBRATIONAL STATES
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Date
2007
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Ohio State University
Abstract
Hirota and Endo reported observations of the rotational transitions of HCO$^+$ and DCO$^+$ in excited vibrational states.} The lowest three rotational transitions of $(02^20)$ could not be detected in their experiment. They ascribed this non-observation to the Stark broadening caused by the electric field in a hollow cathode discharge. More recently Dore and coworkers} also did not see the $\ell=2$ lines in an extended negative glow discharge and interpreted this result in terms of the Stark effect. However, symmetric top ions such as CH$_3$CNH$^+$ } and SD$_3^+$ } were observed with no difficulty. Also no anomalies were observed for similar lines for HCN } and HNC } produced in an extended negative glow discharge. In the present investigation, we extended the measurements up to 800 GHz. The HCO$^+$ and DCO$^+$ ions were produced in an extended negative glow discharge in a gas mixture of H$_2$ or D$_2$ and CO ( a couple of mTorr each ) in Ar buffer ( 12 mTorr ). The measurements were done mostly at liquid nitrogen temperature. For HCO$^+$, the rotational lines in the excited vibrational levels up to (040) and (002) which are located at about 4300 cm$^{-1}$ above the ground state have been measured. The measurements for DCO$^+$ are not as extensive so far. Our observations confirmed that $(02^20)$ lines and, in general, larger $\ell$ lines in the (030) and (040) states were weaker than expected. However, a most notable result obtained in the present investigation is that some low-$J$ lines of $(02^20)$ have been detected as induced emission for both HCO$^+$ and DCO$^+$. This observation clearly leads to a conclusion that the previous non-observation of low-$J$ lines in $(02^20)$ is not due to the Stark effect, but due to specificity of the reaction mechanism and subsequent collisional relaxation processes. %More details will be presented in the talk.
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Author Institution: Department of Chemistry, Okayama University, Okayama,; Japan 700-8530; Department of Chemistry, University of Waterloo, Waterloo,; ON, Canada N2L 3G1