Comparing absorption from classic tracers of the diffuse interstellar
  medium at optical and radio wavelengths along the same sightlines
  % aims To compare information gained from radio and optical absorption line
profiles from the diffuse interstellar medium along the same sightline %
methods We compare new and existing 21cm HI and 3.4mm HCO+ profiles with
profiles of the optical tracers CaII, NaI, and KI from an unpublished thesis of
Tappe (2004) %results The atoms traced optically are all heavily depleted
compared to a Solar abundance and only the integrated optical depths of HI and
HCO+ correlate well with E(B-V). HCO+ is the species with by far the most
limited kinematic distribution and the narrowest lines followed in order by KI,
HI, NaI and CaII. CaII behaves separately in both column density and kinematics
because it samples broader-lined warmer gas. Tracers of the cold neutral medium
NaI, KI, HI and HCO+ share the same kinematic space statistically without
correlating to nearly the same extent in abundance. N(NaI) and N(KI) are
correlated, as are the integrated optical depths of HI and HCO+ but abundance
correlations between optical and radio tracers are not seen. In the only
direction with a measured CH+ profile, a 2 km/s velocity shift between CH+ and
CH, usually interpreted as the sign of shocked gas, is mimicked in the shift of
HI relative to HCO+. CH and HCO+ appear in the ratios N(CH)/N(HCO+)=14.6 and
21.1 along the two sightlines with optically-measured N(CH),compared with a
mean of 12 determined previously at radio and submillimeter wavelengths.
