Current limitations in radio-astronomical spectrometry analysis of local interstellar cloud's hyperfine structures
The first thing to notice is that the Local Interstellar Cloud, in which the Sun is evolving right now, is a fairly diffuse region, with a typical density of about one to a few particles per cubic centimeters. Clouds with such low density are actually mostly atomic; as you can see on this plot (Snow &amp; McCall 2006, adapted from Neufeld et al. 2005):


It is then quite challenging to observe molecules in this region.

Good news is, there is not only molecular lines to give informations about the physical properties (temperature, density, ionization, velocity structure and morphology) of the Local Interstellar Cloud. In particular, ultraviolet is a perfectly suited wavelength range to sudy this region in absorption, and there are some quite extensive studies of the subject (see for example Paper I, Paper II, Paper III and Paper IV of Redfield et al.).