Details

Autor(en) / Beteiligte

• Markelov, Danil A
• Kozinenko, Vitaly P
• Knecht, Stephan
• Kiryutin, Alexey S
• Yurkovskaya, Alexandra V
• Ivanov, Konstantin L

Titel

Singlet to triplet conversion in molecular hydrogen and its role in parahydrogen induced polarization

Ist Teil von

• Physical chemistry chemical physics : PCCP, 2021-09, Vol.23 (37), p.2936-2944

Ort / Verlag

Cambridge: Royal Society of Chemistry

Erscheinungsjahr

2021

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• Detailed experimental and comprehensive theoretical analysis of singlet-triplet conversion in molecular hydrogen dissolved in a solution together with organometallic complexes used in experiments with parahydrogen (the H 2 molecule in its nuclear singlet spin state) is reported. We demonstrate that this conversion, which gives rise to formation of orthohydrogen (the H 2 molecule in its nuclear triplet spin state), is a remarkably efficient process that strongly reduces the resulting NMR (nuclear magnetic resonance) signal enhancement, here of 15 N nuclei polarized at high fields using suitable NMR pulse sequences. We make use of a simple improvement of traditional pulse sequences, utilizing a single pulse on the proton channel that gives rise to an additional strong increase of the signal. Furthermore, analysis of the enhancement as a function of the pulse length allows one to estimate the actual population of the spin states of H 2 . We are also able to demonstrate that the spin conversion process in H 2 is strongly affected by the concentration of 15 N nuclei. This observation allows us to explain the dependence of the 15 N signal enhancement on the abundance of 15 N isotopes. In SABRE experiments at a high magnetic field, the spin order of molecular hydrogen is not just the singlet order, but a combination of singlet and central triplet ones. Additional proton pulse in some cases increases enhancement more than 10-fold.