The gas-phase reactions between HOchi and NOchi are critical in determining the chemical composition of both the troposphere and stratosphere. They dominate both interconversion among radical species and formation of stable reservoir species for both HOchi acid NOchi. In many cases, the rates of these reactions are known, but the products and mechanisms are less well understood. In particular, the distribution of products among available channels as a function of temperature and pressure is very uncertain for several crucial reactions. One important reaction is that of OH with NO2; some fraction of reactions may lead to an isomer of nitric acid, peroxynitrous acid (HOONO), though this species has not been observed in the gas phase. We present an investigation of that possibility. With reaction modulation FTIR spectroscopy in our high-pressure flow system, we are able to examine the behavior of various (HOchi + NO2 --> products) reactions with independent control over system temperature and pressure. Application of strict mass-balance in our wall-less reactor allows for quantitative analysis of reactant and product concentrations, even in those cases where the integrated bandwidths are unavailable. We examine the reactions HO2 + NO2 --> HOONO2 and OH + NO2 --> products. Each reaction proceeds through at least one vibrationally excited intermediate, and in each case there is a potential for the dynamics of those intermediates to produce unexpected behavior. In the case of HO2 + NO2, there is no evidence that a hydrogen atom transfer in the intermediate produces any HONO, even at low pressure. This is consistent with previous work. In the case of OH + NO2 there are almost certainly two intermediates, HOONO and HONO2, but we see no evidence for stable HOONO formation, even at 230 K.