Experimental and Theoretical Studies of the Isotope Exchange Reaction D+H3+→H2D++H{\rm{D}}+{{\rm{H}}}{3}^{+}\to {{\rm{H}}}{2}{{\rm{D}}}^{+}+{\rm{H}}D+H3+→H2D++H (original) (raw)
Related papers
2015
The results of the laboratory study of reaction rate coefficients of several ion-molecule reactions with atomic and molecular hydrogen and molecular deuterium at low temperatures are presented in the thesis. The reaction rate coefficients of the N+ and H+ reaction with H2 were measured with respect to the nuclear spin configuration and rotational excitation of H2. The reactions of anions were a subject of the isotope exchange and isotope effect study. The measurements of the rate coefficients of H2O and D2O formation in the reaction of O– with H2 and D2, isotope exchange reactions OH– + D2 and OD– + H2, and associative detachment and charge transfer channels of D– + H interaction were performed. Experiments were carried out using an AB-22PT instrument with an ion trap. It has producing, guiding, trapping, and detecting systems for ions and a separate source of atomic H. The cooling system allowed to measure the temperature dependencies of the reaction rate coefficients at temperatur...
Formation of H3- by radiative association of H2 and H- in the interstellar medium
Physical Review A, 2011
We develop the theory of radiative association of an atom and a diatomic molecule within a close-coupling framework. We apply it to the formation of H$_3^-$ after the low energy collision (below 0.5 eV) of H$_2$ with H$^-$. Using recently obtained potential energy and permanent dipole moment surfaces of H$_3^-$, we calculate the lowest rovibrational levels of the H$_3^-$ electronic ground state, and the cross section for the formation of H$_3^-$ by radiative association between H$^-$ and ortho- and para-H$_2$. We discuss the possibility for the H$_3^-$ ion to be formed and observed in the cold and dense interstellar medium in an environment with a high ionization rate. Such an observation would be a probe for the presence of H$^-$ in the interstellar medium.
C + in the Interstellar Medium: Collisional Excitation by H 2 Revisited
The Astrophysical Journal, 2014
C + is a critical constituent of many regions of the interstellar medium, as it can be a major reservoir of carbon and, under a wide range of conditions, the dominant gas coolant. Emission from its 158 µm fine structure line is used to trace the structure of photon dominated regions in the Milky Way and is often employed as a measure of the star formation rate in external galaxies. Under most conditions, the emission from the single [Cii] line is proportional to the collisional excitation rate coefficient. We here used improved calculations of the deexcitation rate of [Cii] by collisions with H 2 to calculate more accurate expressions for interstellar C + fine structure emission, its critical density, and its cooling rate. The collision rates in the new quantum calculation are ∼ 25% larger than those previously available, and narrow the difference between rates for excitation by atomic and molecular hydrogen. This results in [Cii] excitation being quasi-independent of the molecular fraction and thus dependent only on the total hydrogen particle density. A convenient expression for the cooling rate at temperatures between 20 K and 400 K, assuming an LTE H 2 ortho to para ration is Λ(LTE OPR) = 11.5 + 4.0 e −100 K/T kin e −91.25 K/T kin n(C +) n(H 2) × 10 −24 ergs cm −3 s −1. The present work should allow more accurate and convenient analysis of the [Cii] line emission and its cooling.
Astronomy and Astrophysics, 2001
Although deuterium isotope fractionation in cold, dark interstellar clouds is reasonably well understood via gas-phase chemistry, there are some discrepancies between observation and theory. For example, the observed abundance ratio between the deuterated species C3HD and the cyclic molecule C3H2 is significantly higher than most theoretical values unless the exchange reaction C3H + 3 + HD −→ C3H2D + + H2 is efficient. In this paper, we report quantum chemical and dynamical calculations on this reaction, which show it to possess a large activation energy barrier and to be very slow at all normal interstellar temperatures.
Deuterated interstellar and circumstellar molecules: D/H ratio and dominant formation processes
There are several constraints associated with the different models used in accounting for the D/H ratio observed of singly and multiply deuterated interstellar and circumstellar molecular species. Thermodynamically, the most distinctive difference between a molecule and its deuterated analogue is the zero point energy (ZPE). Applying high level quantum chemical calculations, the ZPE for all H-containing and their corresponding D-analogues for all interstellar/circumstellar molecular species considered in this study are determined. From the difference in the ZPE between the H-containing and the corresponding D-analogue, Boltzmann factor is computed for all the systems using the excitation tempera-ture/molecular cloud temperature for the known D-molecules and a range of temperature for others. From the results, there is a direct correlation between the Boltzmann factors and the D/H ratios. Pronounced deuterium fractionation occurs at larger values of Boltzmann factor resulting in the observed high D/H ratios. Increased deuterium fractionation at low temperature suggests that grain surface reactions are the major formation processes for deuterated molecules. This implies that at lower temperature (higher Boltzmann factor), the exchange reaction involving deuterium or deuterium fractionation is much pronounced resulting in the distribution and redistribution of deuterium among various species. The implications of these results and the possibility of detecting more D-molecules are discussed. Graphic abstract
Dynamics of the isotope exchange reaction of D with H3+, H2D+, and D2H+
The Journal of Chemical Physics, 2021
We have measured the merged-beams rate coefficient for the titular isotope exchange reactions as a function of the relative collision energy in the range of ∼3 meV-10 eV. The results appear to scale with the number of available sites for deuteration. We have performed extensive theoretical calculations to characterize the zero-point energy corrected reaction path. Vibrationally adiabatic minimum energy paths were obtained using a combination of unrestricted quadratic configuration interaction of single and double excitations and internally contracted multireference configuration interaction calculations. The resulting barrier height, ranging from 68 meV to 89 meV, together with the various asymptotes that may be reached in the collision, was used in a classical over-the-barrier model. All competing endoergic reaction channels were taken into account using a flux reduction factor. This model reproduces all three experimental sets quite satisfactorily. In order to generate thermal rate coefficients down to 10 K, the internal excitation energy distribution of each H + 3 isotopologue is evaluated level by level using available line lists and accurate spectroscopic parameters. Tunneling is accounted for by a direct inclusion of the exact quantum tunneling probability in the evaluation of the cross section. We derive a thermal rate coefficient of < 1 × 10 −12 cm 3 s −1 for temperatures below 44 K, 86 K, and 139 K for the reaction of D with H + 3 , H 2 D + , and D 2 H + , respectively, with tunneling effects included. The derived thermal rate coefficients exceed the ring polymer molecular dynamics prediction of Bulut et al. [J. Phys. Chem. A 123, 8766 (2019)] at all temperatures.
Journal of Chemical Physics, 2020
We report a large set of state-to-state rate constants for the H + HD reactive collision, using Quasi-Classical Trajectory (QCT) simulations on the accurate H 3 global potential energy surface of Mielke et al. [J. Chem. Phys. 116, 4142 (2002)]. High relative collision energies (up to ≈56 000 K) and high rovibrational levels of HD (up to ≈50 000 K), relevant to various non thermal equilibrium astrophysical media, are considered. We have validated the accuracy of our QCT calculations with a new efficient adaptation of the Multi Configuration Time Dependent Hartree (MCTDH) method to compute the reaction probability of a specific reactive channel. Our study has revealed that the high temperature regime favors the production of H 2 in its highly rovibrationnally excited states, which can de-excite radiatively (cooling the gas) or collisionally (heating the gas). Those new state-to-state QCT reaction rate constants represent a significant improvement in our understanding of the possible mechanisms leading to the destruction of HD by its collision with a H atom.
Molecular Hydrogen Formation in the Interstellar Medium
The Astrophysical Journal, 2002
We have developed a model for molecular hydrogen formation under astrophysically relevant conditions. This model takes fully into account the presence of both physisorbed and chemisorbed sites on the surface, allows quantum mechanical diffusion as well as thermal hopping for absorbed H-atoms, and has been benchmarked versus recent laboratory experiments on H 2 formation on silicate surfaces. The results show that H 2 formation on grain surface is efficient in the interstellar medium up to some 300K. At low temperatures (≤100K), H 2 formation is governed by the reaction of a physisorbed H with a chemisorbed H. At higher temperatures, H 2 formation proceeds through reaction between two chemisorbed H atoms. We present simple analytical expressions for H 2 formation which can be adopted to a wide variety of surfaces once their surfaces characteristics have been determined experimentally.
2024
We present a merged-beams study of reactions between HD þ ions, stored in the Cryogenic Storage Ring (CSR), and laser-produced ground-term C atoms. The molecular ions are stored for up to 20 s in the extreme vacuum of the CSR, where they have time to relax radiatively until they reach their vibrational ground state (within 0.5 s of storage) and rotational states with J ≤ 3 (after 5 s). We combine our experimental studies with quasiclassical trajectory calculations based on two reactive potential energy surfaces. In contrast to previous studies with internally excited H þ 2 and D þ 2 ions, our results reveal a pronounced isotope effect, favoring the production of CH þ over CD þ across all collision energies, and a significant increase in the absolute rate coefficient of the reaction. Our experimental results agree well with our theoretical calculations for vibrationally relaxed HD þ ions in their lowest rotational states.