H₂ clumped isotope measurements at natural isotopic abundances

Abstract

Rationale Molecular hydrogen (H 2 ) is an important gas for atmospheric chemistry, and an indirect greenhouse gas due to its reaction with OH. The isotopic composition of H 2 (δD) has been used to investigate its atmospheric budget; here we add a new observable, the clumped isotopic signature ΔDD, to the tools that can be used to study the global cycle of H 2 . Methods A method for determining ΔDD in H 2 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 H 3 + and H 2 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 H 2 at natural isotopic abundances, with a precision that is adequate for observing the expected variations in atmospheric and other natural H 2 . This method opens the road to new research on the natural H 2 cycle.

Optical clumped isotope thermometry of carbon dioxide

“…At 300 K the ZPE difference factor deviates from unity by 5 parts in 10 6 if Δ ν 0 = 0.001 cm −1 . This implies that an uncertainty of a few ppm – a range that will be amenable to measurements in the near future – is sufficient to determine ZPE differences at the 0.001 cm −1 uncertainty level, irrespective whether the ZPE differences are large, as in the case of the H 2 + D 2 2 HD reaction where Δ ν 0 = 54.867 cm −1 50 , 51 , or small – as in reaction R1 , where calculated values 22 , 33 , 34 range from 0.433 to 0.435 cm −1 .…”

“…abundance n i /Σ j n j (mol/mol)Rel. contribution to mass (%)NoteNoSymbol1 12 C 16 O 2 449.842 ⋅ 10 −1 100.0002 13 C 16 O 2 451.100 ⋅ 10 −2 93.6363 12 C 16 O 18 O463.947 ⋅ 10 −3 99.7854 12 C 16 O 17 O457.478 ⋅ 10 −4 6.364b5 13 C 16 O 18 O474.413 ⋅ 10 −5 96.7106 13 C 16 O 17 O468.361 ⋅ 10 −6 0.2117 12 C 18 O 2 483.957 ⋅ 10 −6 99.578c8 12 C 17 O 18 O471.500 ⋅ 10 −6 3.2869 12 C 17 O 2 461.421 ⋅ 10 −7 0.00410 13 C 18 O 2 494.424 ⋅ 10 −8 100.00011 13 C 17 O 18 O481.676 ⋅ 10 −8 0.42212 13 C 17 O 2 471.588 ⋅ 10 −9 0.003Abundance values are based on assuming a statistical distribution of oxygen and carbon isotopes in international standard materials (VSMOW for O and VPDB for C: 13 R = 11056/988944, 17 R = 3790/9976206, 18 R = 20004/9976206) 53 . a Atomic mass constant.…”

“…Abundance values are based on assuming a statistical distribution of oxygen and carbon isotopes in international standard materials (VSMOW for O and VPDB for C: 13 R = 11056/988944, 17 R = 3790/9976206, 18 R = 20004/9976206) 53 . a Atomic mass constant.…”

Clumped 13CH2D and 12CHD2 compositions of methyl groups from wood and synthetic monomers: Methods, experimental and theoretical calibrations, and initial results

“…As is generally the case when establishing new clumped isotope measurements, there are no standards available with independently known D13 CH 2 D and D12 CHD 2 . A common approach for clumped isotopic standardization is to equilibrate samples at known temperatures in order to place D values in a thermodynamic reference frame (e.g., Ghosh et al, 2006;Dennis et al, 2011;Yeung et al, 2012Yeung et al, , 2017Ono et al, 2014;Stolper et al, 2014a;Magyar et al, 2016;Young et al, 2016;Popa et al, 2018). We follow this approach and equilibrate isotopologues of CH 3 Cl on a Pt catalyst (see Fig.…”

Clumped isotope effects of thermogenic methane formation: Insights from pyrolysis of hydrocarbons

“…This mechanism for producing exceptional clumped isotope ∆ values has been called the 'combinatorial effect' (Yeung, 2016;Röckmann et al, 2016;Clog et al, 2018;Cao et al, 2019;Xia and Gao, 2019;Taenzer et al, 2020). Such effects can arise any time two or more symmetrically equivalent molecular sites are created in such a way that they have different probabilities of containing a rare isotope substitution; these anomalies have been observed in microbial methane (Taenzer et al, 2020), and predicted for O 2 , N 2 (Yeung, 2016) and ethane (Clog et al, 2018), and should be expected for emerging clumped isotope systems like sulfate (Ueno et al, 2019;Neubauer et al, 2020), H 2 (Popa et al, 2019), perchlorate (Martin, 2020), nitrate (Neubauer et al, 2020), and ∆ 48 in CO 2 (Fiebig et al, 2019a;Bajnai et al, 2020).…”