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Title: Nuclear relaxation of {sup 3}He in the presence of NO

Abstract

By virtue of the fact that its low-lying {sup 2}{pi}{sub 3/2} state is paramagnetic, nitric oxide (NO) can be an effective agent for inducing nuclear spin relaxation during isolated binary collisions with other species. At the same time, the strong coupling between the electronic angular momentum and the internuclear axis of this particular molecule leads to a situation in which its effective magnetic moment depends critically on molecular motions that take place on the time scale of the collision. Here we present the results of an investigation in which the NMR-detected longitudinal nuclear relaxation rate T{sub 1}{sup -1} of room temperature {sup 3}He gas adulterated with NO was measured as a function of NO density ([NO]) in two different magnetic fields. We find T{sub 1}{sup -1}=0.0502(3)[NO] s{sup -1} at 1.50 T, and T{sub 1}{sup -1}=0.0506(3)[NO] s{sup -1} at 2.35 T, where [NO] is expressed in amagat. Under these conditions approximately two-thirds of the NO molecules occupy the diamagnetic {sup 2}{pi}{sub 1/2} ground state and one-third occupy the paramagnetic {sup 2}{pi}{sub 3/2} state. Our data can be understood in terms of a semiclassical treatment of collision dynamics that involves the paramagnetic moment autocorrelation function.

Authors:
; ; ; ;  [1]
  1. Department of Physics, Simon Fraser University, Burnaby, British Columbia, V5A 1S6 (Canada)
Publication Date:
OSTI Identifier:
20974592
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. A; Journal Volume: 73; Journal Issue: 2; Other Information: DOI: 10.1103/PhysRevA.73.022721; (c) 2006 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
74 ATOMIC AND MOLECULAR PHYSICS; ATOM-MOLECULE COLLISIONS; DENSITY; GROUND STATES; HELIUM 3; MAGNETIC FIELDS; MAGNETIC MOMENTS; MOLECULES; NITRIC OXIDE; NUCLEAR MAGNETIC RESONANCE; PARAMAGNETISM; SEMICLASSICAL APPROXIMATION; SPIN; SPIN-SPIN RELAXATION; STRONG-COUPLING MODEL; TEMPERATURE RANGE 0273-0400 K

Citation Formats

Archibald, G., Brief, E., Lei, C., Pausak, T., and Hayden, M. E. Nuclear relaxation of {sup 3}He in the presence of NO. United States: N. p., 2006. Web. doi:10.1103/PHYSREVA.73.022721.
Archibald, G., Brief, E., Lei, C., Pausak, T., & Hayden, M. E. Nuclear relaxation of {sup 3}He in the presence of NO. United States. doi:10.1103/PHYSREVA.73.022721.
Archibald, G., Brief, E., Lei, C., Pausak, T., and Hayden, M. E. Wed . "Nuclear relaxation of {sup 3}He in the presence of NO". United States. doi:10.1103/PHYSREVA.73.022721.
@article{osti_20974592,
title = {Nuclear relaxation of {sup 3}He in the presence of NO},
author = {Archibald, G. and Brief, E. and Lei, C. and Pausak, T. and Hayden, M. E.},
abstractNote = {By virtue of the fact that its low-lying {sup 2}{pi}{sub 3/2} state is paramagnetic, nitric oxide (NO) can be an effective agent for inducing nuclear spin relaxation during isolated binary collisions with other species. At the same time, the strong coupling between the electronic angular momentum and the internuclear axis of this particular molecule leads to a situation in which its effective magnetic moment depends critically on molecular motions that take place on the time scale of the collision. Here we present the results of an investigation in which the NMR-detected longitudinal nuclear relaxation rate T{sub 1}{sup -1} of room temperature {sup 3}He gas adulterated with NO was measured as a function of NO density ([NO]) in two different magnetic fields. We find T{sub 1}{sup -1}=0.0502(3)[NO] s{sup -1} at 1.50 T, and T{sub 1}{sup -1}=0.0506(3)[NO] s{sup -1} at 2.35 T, where [NO] is expressed in amagat. Under these conditions approximately two-thirds of the NO molecules occupy the diamagnetic {sup 2}{pi}{sub 1/2} ground state and one-third occupy the paramagnetic {sup 2}{pi}{sub 3/2} state. Our data can be understood in terms of a semiclassical treatment of collision dynamics that involves the paramagnetic moment autocorrelation function.},
doi = {10.1103/PHYSREVA.73.022721},
journal = {Physical Review. A},
number = 2,
volume = 73,
place = {United States},
year = {Wed Feb 15 00:00:00 EST 2006},
month = {Wed Feb 15 00:00:00 EST 2006}
}
  • Longitudinal relaxation times T/sub 1/ have been measured in /sup 3/He-/sup 4/He gas mixtures, using pulsed NMR, in the temperature range 0.6-15 K. Helium-3 number densities of the order of 10/sup 24/ atoms m/sup /minus/3/ were used. Relaxation takes place on or near the walls of the Pyrex sample cells and measurements of T/sub 1/ give information about the surface phases. A cryogenic precoating of solid molecular hydrogen was used to reduce the helium-substrate binding energy from approx. 100 K on Pyrex to approx. 13 K for /sup 3/He and 15 K for /sup 4/He. The T/sub 1/ data atmore » high temperatures were similar to those observed previously in the pure /sup 3/He-H/sub 2/ system. The presence of /sup 4/He generally caused T/sub 1/ to rise on cooling below 2 K due to the preferential adsorption of /sup 4/He over /sup 3/He at the surface. However, /sup 3/He atoms that go into quasiparticle states in the superfluid helium film can be an extra source of relaxation. In uncleaned cells, relaxation probably takes place in quasiparticle states at the free surface of the superfluid film, which are bound with an energy of 5.1 /plus minus/ 0.3 K. Baking the Pyrex cells under vacuum and rf discharge cleaning the walls before sealing in the sample gas were found to increase the bulk gas T/sub 1/ by two or three orders of magnitude. In a cleaned, sealed cell of T/sub 1/ of approx. 8 h was measured at 7.7 MHz and 0.8 K. In this case relaxation is probably occurring two or three helium layers away from the helium-hydrogen interface. It may be possible to observe a predicted minimum in the intrinsic dipolar T/sub 1/ of the bulk gas by using a /sup 4/He wall coating to suppress wall relaxation effects (which usually dominate the nuclear relaxation of the bulk gas).« less
  • Longitudinal relaxation times T/sub 1/ have been measured in /sup 3/He gas, using pulsed NMR, for number densities between 3 /times/ 10/sup 23/ and 6 /times/ 10/sup 25/ spins m/sup /minus/3/ and temperatures between 0.6 and 15 K. Relaxation takes place on or near the walls of the Pyrex sample cells and measurements of T/sub 1/ give information about the surface phases. A cryogenic wall coating of solid molecular hydrogen was found to delay the formation of a /sup 3/He monolayer on cooling, and T/sub 1/ measurements were consistent with a binding energy of approx. 13 K for a /supmore » 3/He atom to a hydrogen surface. At temperatures below approx. 2 K a completed /sup 3/He monolayer forms on the H/sub 2/ coating. No variation of the areal density of monolayer completion with bulk number density at fixed temperature could be observed and the completed /sup 3/He monolayer is thought to be a dense fluid. Baking the Pyrex sample cells under vacuum and using an rf discharge in /sup 3/He gas to clean the walls before sealing in the sample gas were found to increase the observed T/sub 1/'s by up to three orders of magnitude. Once a /sup 3/He monolayer has formed on the H/sub 2/ surface in these cleaned, sealed cells, the dipolar interaction between adsorbed spins is thought to be the dominant source of longitudinal relaxation. The data are consistent with a dipolar relaxation model with a correlation time of approx. 2 /times/ 10/sup /minus/9/ sec. This time is long compared to the value of 10/sup /minus/11/ or 10/sup /minus/12/ sec in the 3D fluid. This suggests that if the surface phase is a 2D fluid and the dipolar mechanism is indeed the dominant one, then the atoms in the 2D fluid are less mobile than in three dimensions. This is consistent with recent susceptibility measurements.« less