Isotopic fractionation in interstellar molecules

Abstract

The level of isotopic fractionation in molecules provides insights into their formation environments and how they formed. In this article, we review hydrogen and nitrogen isotopic fractionation in low-mass star-forming regions. Interstellar molecules are significantly enriched in deuterium. The importance of the nuclear spin states of light species on deuterium fractionation and the usefulness of singly and doubly deuterated molecules as chemical tracers are discussed. Observations have revealed that molecules in prestellar cores are enriched in or depleted in 15 N depending on molecules. Compared with deuterium fractionation chemistry, our understanding of 15 N fractionation chemistry is not well established. We briefly discuss potential 15 N fractionation routes, i.e., isotopic-exchange reactions and isotopic selective photodissociation of N2. In addition, the selective freeze-out of 15 N atoms onto dust grains around the transition between N atoms and N2 is discussed as a potential mechanism that causes the depletion of 15 N in the gas phase.

Quantum Tunnelling Driven H2 Formation on Graphene

“…Based on the Bell–Limbach tunnelling model, the formation rate of D 2 would be more than 6 orders of magnitude lower than the formation rates of H 2 . These results are in line with the current understanding that in outer space the isotopic fractionation of deuterium goes through a different path involving other larger molecules . The strong isotope effects also suggest that delicate isotopic control of H 2 formation may be achievable.…”

“…These results are in line with the current understanding that in outer space the isotopic fractionation of deuterium goes through a different path involving other larger molecules. 58 The strong isotope effects also suggest that delicate isotopic control of H 2 formation may be achievable.…”

Complex Organic Molecules Detected in 12 High-mass Star-forming Regions with Atacama Large Millimeter/submillimeter Array

“…The level of fractionations of COMs is sensitive to the density, temperature, and timescale so that they provide insight of when and where they are formed. There are a few mechanisms that can alter the isotopic ratios, including isotopic exchange reactions both in the gas and ice phases, selective photodissociations, and timescale spending at cold temperature (Furuya 2018;Jørgensen et al 2020;Öberg & Bergin 2021). From our data sets, we examine the hydrogen, carbon, oxygen, and nitrogen isotopic ratios.…”

Quantum tunnelling driven H$_2$ formation on graphene

“…These results are in line with the current understanding that in outer space the isotopic fractionation of deuterium goes through a different path involving other larger molecules. 58 The strong isotope effects also suggest that delicate isotopic control of H 2 formation may be achievable. The previous sections discussed the H 2 formation rates from H dimers, which corresponds to the situation in the sparse-coverage limit.…”