Resolving Gas Chemistry at Arcsecond Scales in Nearby Spiral Nuclei

Astrochemistry is rapidly becoming one of the most powerful tools to study the structure and evolution of the central kiloparsec in spiral nuclei. Imagining the distribution of quiescent ion-molecule, photon-dominated region (PDR) and shock chemistry permits the triggers of nuclear starbursts to be identified and the bursts subsequent feedback to be constrained. Two new chemical methods for identifying the evolutionary phase of the starbursts in IC 342, NGC 6946 and Maffei 2 are discussed. The first method is to use the HCO+/N2H+ ratio to constrain the degree of penetration of dense clumps by UV radiation. The second determines the evolutionary phase by mapping the amount and physical conditions of the densest molecular component via multi-transition HC3N observations. With the full capabilities of radio facilities such as the VLA and ALMA, probing the changing gas chemistry on sub arcsecond scales in external galaxies will very soon be routine.