Conclusions
We have established a method for determining ΔDD in H2 at natural isotopic abundances, with a precision that is adequate for observing the expected variations in atmospheric and other natural H2 . This method opens the road to new research on the natural H2 cycle.
Methods
A method for determining ΔDD in H2 was developed using the high-resolution MAT 253-Ultra isotope ratio mass spectrometer (Thermo Fisher). The HH, HD and DD abundances are quantified at medium resolution (M/ΔM ≈ 6000), which is sufficient for HD+ and DD+ to be distinguished from H3 + and H2 D+ , respectively. The method involves sequential measurement of isotopologues, and DD is measured using an ion counter. For verification, catalytic ΔDD equilibration experiments were performed at temperatures of up to 850°C.
Results
The typical precision obtained for ΔDD is 2-6‰, close to the theoretical counting statistics limit, and adequate for detecting the expected natural variations. Compatibility and medium-term reproducibility are consistent with the precision values. The method was validated using temperature equilibration experiments, which showed a dependence of ΔDD on temperature as expected form theoretical calculations. Conclusions: We have established a method for determining ΔDD in H2 at natural isotopic abundances, with a precision that is adequate for observing the expected variations in atmospheric and other natural H2 . This method opens the road to new research on the natural H2 cycle.