July 2017

Lithium Hydride

As a result of a recent study, the detection of lithium hydride (LiH) has been called into question. Combes & Wiklink reported a very tentative detection of LiH in 1998 on the basis of a single rotational line. Since this transition normally falls into a spectral region that is opaque due to atmospheric absorption, they looked for it toward the quasar B0218+357, where the line would be redshifted to a higher frequency that falls in one of the transparent windows of the atmosphere. Even with this advantage, the line observed by Combes & Wiklink was very weak.

Researcher Links
DA Neufeld
P Goldsmith
C Comito
A Schmiedeke

In 2011, Friedel and coworkers again sought to observe LiH toward B0128+357 and two additional quasars, PKS1820-211 and PKS0201-113, using CARMA. They observed the same very weak feature toward B0128+357 but not toward the other two sources.

Recently, Neufeld and coworkers used the much more sensitive Atacama Large Millimeter Array to search for LiH toward sources within our galaxy, Sgr B2(Main) and W49N, and were not able to find it. They note that the upper limits for the abundance of LiH imposed by their attempt to observe the molecule are much smaller than those implied by the previous studies and argue that perhaps "... the previously reported tentative detections ... are in fact spurious."

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