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While the growing realization of the importance of long-range interactions is being demonstrated in cold and ultracold bimolecular collision experiments, their influence on one of the most critical ion-neutral reactions has been overlooked. Here, we address the non-Langevin abrupt decrease observed earlier in the low energy integral cross sections and rate coefficients of the astrochemically important H + HeH$^+$ $\rightarrow$ H$^+_2$ + He reaction. We attribute this to the presence of artificial barriers on existing potential energy surfaces (PESs). By incorporating precise long-range interaction terms, we introduce a new refined barrierless PES for the electronic ground state of HeH$_{2}^{+}$ reactive system, aligning closely with high level {\ab} electronic energies. Our findings, supported by various classical, quantum, and statistical methods, underscore the significance of long-range terms in accurately modeling reactive PESs. The low temperature rate coefficient on this new PES shows a substantial enhancement as compared to the previous results and aligns with Langevin behavior. This enhancement could affect noticeably the impact HeH$^{+}$ abundance prediction in early Universe condition.

To test the hypothesis that amino acids, the molecular precursors of life, could have reached primitive Earth embedded in icy grains of space transported by comets or asteroids, we are combining a DFT study of the decarboxylation and deamination of glycine—neutral, singly, and doubly ionized—with a RT-TDDFT study of the same neutral and charged glycine interacting with ionizing radiation. In all cases, the molecules are surrounded by water molecules, mimicking the icy environment. The outcomes of this study will be presented.

Growing innovations in recent experimental studies of cold and ultracold gas-phase bimolec- ular collisions have demonstrated the importance of long-range interactions in ion-neutral reactions [1]. In this study, we address the non-Langevin abrupt decrease observed ear- lier [2,3] in the low energy integral cross sections and rate coefficients of astrochemically important H + HeH+ ! H+ 2 + He reaction. We attribute this to the presence of artificial barriers on existing potential energy surfaces (PESs) [4]. By including precise long-range interaction terms, we introduce a new refined barrierless PES for the HeH+ 2 reactive system, aligning closely with high level ab initio electronic energies. Our findings, supported by various classical, quantum, and statistical methods, underscore the significance of long- range terms in accurately modeling reactive PESs. Moreover, the substantial enhancement in rate coefficients at low temperatures (roughly 2 orders of magnitude at 10 K), which conform with Langevin behavior, may have significant impact on the HeH+ abundance prediction in early Universe condition, which are further to be discovered. Most notably, this enhancement yields a reaction rate coefficient of comparable magnitude to that observed in a recent experiment [5] on dissociative recombination (DR) of HeH+, particularly within 100 K. This suggests that the destruction of primordial HeH+ by H may become as significant as the DR process at low redshifts.

Dissociative recombination of N$_2$H$^+$ is explored in a two-step theoretical study. In a first step, a diatomic (1D) rough model with frozen NN bond and frozen angles is adopted, in the framework of the multichannel quantum defect theory (MQDT). The importance of the indirect mechanism and of the bending mode is revealed, in spite of the disagreement between our cross section and the experimental one. In a second step, we use our recently elaborated 3D approach based on the normal mode approximation combined with R-matrix theory and MQDT. This approach results in satisfactory agreement with storage-ring measurements, significantly better at very low energy than the former calculations.