The Ultraviolet to Near‐Infrared Optical Properties of Polycyclic Aromatic Hydrocarbons: A Semiempirical Model

Interstellar polycyclic aromatic hydrocarbon (PAH) infrared emission features represent an important and unique diagnostic tool of the chemical and physical conditions throughout the universe. However, one challenge facing the widely accepted PAH emission model has been the detection of infrared features in regions of low UV flux. Using recently published laboratory near-infrared (NIR) PAH ion absorption data measured in our laboratory, we build on previous models for PAH ion absorption in the UV-visible to extrapolate a new model that incorporates PAH ion absorption in the NIR. This model provides a basis for comparing the relative energy absorption of PAH ions in the UV-visible and NIR regions for a wide variety of stellar types. This model demonstrates that the radiation from late- type stars can pump the mid-IR PAH features. Subject headinggs: astrochemistry — infrared: ISM — ISM: molecules — methods: laboratory — molecular processes — techniques: spectroscopic