Graninger, DawnHerbst, EricOberg, KarinVasyunin, Anton I.2015-09-112014Graninger, Dawn M., Eric Herbst, Karin I. Öberg, and Anton I. Vasyunin. 2014. “The HNC/HCN Ratio in Star-Forming Regions.” The Astrophysical Journal 787, no. 1: 74. doi:10.1088/0004-637x/787/1/740004-637Xhttp://nrs.harvard.edu/urn-3:HUL.InstRepos:22556373HNC and HCN, typically used as dense gas tracers in molecular clouds, are a pair of isomers that have great potential as a temperature probe because of temperature dependent, isomer-specific formation and destruction pathways. Previous observations of the HNC/HCN abundance ratio show that the ratio decreases with increasing temperature, something that standard astrochemical models cannot reproduce. We have undertaken a detailed parameter study on which environmental characteristics and chemical reactions affect the HNC/HCN ratio and can thus contribute to the observed dependence. Using existing gas and gas-grain models updated with new reactions and reaction barriers, we find that in static models the H + HNC gas-phase reaction regulates the HNC/HCN ratio under all conditions, except for very early times. We quantitatively constrain the combinations of H abundance and H + HNC reaction barrier that can explain the observed HNC/HCN temperature dependence and discuss the implications in light of new quantum chemical calculations. In warm-up models, gas-grain chemistry contributes significantly to the predicted HNC/HCN ratio and understanding the dynamics of star formation is therefore key to model the HNC/HCN system.en-USJournal Article2015-08-08Graninger, D., Herbst, E., Öberg, K.I., Vasyunin, A.2015-09-1110.1088/0004-637x/787/1/74