TY - JOUR

T1 - Singlet to triplet conversion in molecular hydrogen and its role in parahydrogen induced polarization

AU - Markelov, Danil A.

AU - Kozinenko, Vitaly P.

AU - Knecht, Stephan

AU - Kiryutin, Alexey S.

AU - Yurkovskaya, Alexandra V.

AU - Ivanov, Konstantin L.

N1 - Funding Information: Financial support for the theoretical part by the Russian Science Foundation (grant No. 20-62-47038) is gratefully acknowledged. We acknowledge the Ministry of Science and Education of RF (contract No. 075-15-2021-580) for providing financial support for the experimental work at ITC. Prof. Geoffrey Bodenhausen (ENS, Paris) suggested several editorial changes. Prof. Konstantin L. Ivanov passed away on the 5th of March, 2021 at the age 44. In his early career, he made major contributions to the theory of chemical reaction kinetics in liquid phase. Later, he significantly contributed to unraveling the mechanisms of light-induced nuclear hyperpolarization in liquids and solid state using the concept of level anti-crossing (LAC). In recent years, his main research efforts, both theoretical and experimental, were concentrated on spin and chemical dynamics in PHIP and SABRE methods using LAC; for this, he was awarded the Günther Laukien Prize in 2020. He also was the scientific PhD adviser of two authors (DAM and VPK). Theoretical explanation of singlet to triplet conversion of nuclear spins molecular hydrogen and its experimental verification was his last project. He worked on this manuscript shortly before being deadly infected. Publisher Copyright: © 2021 the Owner Societies.

PY - 2021/10/7

Y1 - 2021/10/7

N2 - 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 H2 molecule in its nuclear singlet spin state) is reported. We demonstrate that this conversion, which gives rise to formation of orthohydrogen (the H2 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 15N 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 H2. We are also able to demonstrate that the spin conversion process in H2 is strongly affected by the concentration of 15N nuclei. This observation allows us to explain the dependence of the 15N signal enhancement on the abundance of 15N isotopes.

AB - 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 H2 molecule in its nuclear singlet spin state) is reported. We demonstrate that this conversion, which gives rise to formation of orthohydrogen (the H2 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 15N 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 H2. We are also able to demonstrate that the spin conversion process in H2 is strongly affected by the concentration of 15N nuclei. This observation allows us to explain the dependence of the 15N signal enhancement on the abundance of 15N isotopes.

UR - http://www.scopus.com/inward/record.url?scp=85116565999&partnerID=8YFLogxK

U2 - 10.1039/d1cp03164c

DO - 10.1039/d1cp03164c

M3 - Article

C2 - 34542122

AN - SCOPUS:85116565999

VL - 23

SP - 20936

EP - 20944

JO - Physical Chemistry Chemical Physics

JF - Physical Chemistry Chemical Physics

SN - 1463-9076

IS - 37

ER -