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We present a comprehensive analysis of interstellar absorption lines seen inmoderately-high resolution, high signal-to-noise ratio optical spectra of SN2014J in M82. Our observations were acquired over the course of six nights,covering the period from ~6 days before to ~30 days after the supernova reachedits maximum B-band brightness. We examine complex absorption from Na I, Ca II,K I, Ca I, CH+, CH, and CN, arising primarily from diffuse gas in theinterstellar medium (ISM) of M82. We detect Li I absorption over a range invelocity consistent with that exhibited by the strongest Na I and K Icomponents associated with M82; this is the first detection of interstellar Liin a galaxy outside of the Local Group. There are no significant temporalvariations in the absorption-line profiles over the 37 days sampled by ourobservations. The relative abundances of the various interstellar speciesdetected reveal that the ISM of M82 probed by SN 2014J consists of a mixture ofdiffuse atomic and molecular clouds characterized by a wide range ofphysical/environmental conditions. Decreasing N(Na I)/N(Ca II) ratios andincreasing N(Ca I)/N(K I) ratios with increasing velocity are indicative ofreduced depletion in the higher-velocity material. Significantcomponent-to-component scatter in the N(Na I)/N(Ca II) and N(Ca I)/N(Ca II)ratios may be due to variations in the local ionization conditions. An apparentanti-correlation between the N(CH+)/N(CH) and N(Ca I)/N(Ca II) ratios can beunderstood in terms of an opposite dependence on gas density and radiationfield strength, while the overall high CH+ abundance may be indicative ofenhanced turbulence in the ISM of M82. The Li abundance also seems to beenhanced in M82, which supports the conclusions of recent gamma-ray emissionstudies that the cosmic-ray acceleration processes are greatly enhanced in thisstarburst galaxy.

Diffuse Atomic and Molecular Gas in the Interstellar Medium of M82 toward SN 2014J