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. 2016 Dec 23;6:38492.
doi: 10.1038/srep38492.

Collisional Cross-Section of Water Molecules in Vapour Studied by Means of 1 H Relaxation in NMR

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Collisional Cross-Section of Water Molecules in Vapour Studied by Means of 1 H Relaxation in NMR

Daniele Mammoli et al. Sci Rep. .
Free PMC article


In gas phase, collisions that affect the rotational angular momentum lead to the return of the magnetization to its equilibrium (relaxation) in Nuclear Magnetic Resonance (NMR). To the best of our knowledge, the longitudinal relaxation rates R1 = 1/T1 of protons in H2O and HDO have never been measured in gas phase. We report R1 in gas phase in a field of 18.8 T, i.e., at a proton Larmor frequency ν0 = 800 MHz, at temperatures between 353 and 373 K and pressures between 9 and 101 kPa. By assuming that spin rotation is the dominant relaxation mechanism, we estimated the effective cross-section σJ for the transfer of angular momentum due to H2O-H2O and HDO-D2O collisions. Our results allow one to test theoretical predictions of the intermolecular potential of water in gas phase.


Figure 1
Figure 1. (Points) Experimental rates R1 of gaseous H2O at 800MHz and at pressures 9 < p < 101 kPa.
(Lines) Estimates of R1 arising from spin-rotation, using Eq. 1 with the parameters in Table 2.
Figure 2
Figure 2. Schematic view of the coaxial tubes: outer tube (10 mm outer diameter) filled with toluene-d8 and inner tube (5 mm outer diameter, held by Teflon spacers) containing water vapour sealed under vacuum.
Figure 3
Figure 3. Proton NMR spectra of samples described in Fig. 2 at 800MHz and at 300K (top) or 363K (bottom).
The signals at 2.1 and 7 ppm are attributed to residual protons in incompletely deuterated toluene-d8. The signal at 3.2 stems from water in gas phase. Small peaks between 0.3 and 2 ppm are due to impurities in toluene-d8. We diluted TMS in toluene-d8 to use its resonance at 0 ppm as chemical shift reference.

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