EPR study of NO radicals encased in modified open C<sub>60</sub> fullerenes

Abstract

Abstract. Using pulsed electron paramagnetic resonance (EPR) techniques, the low-temperature magnetic properties of the NO radical being confined in two different modified open C60-derived cages are determined. It is found that the smallest principal g value g3, being assigned to the axis of the radical, deviates strongly from the free electron value. This behaviour results from partial compensation of the spin and orbital contributions to the g3 value. The measured g3 values in the range of 0.7 yield information about the deviation of the locking potential for the encaged NO from axial symmetry. The estimated 17 meV asymmetry is quite small compared to the situation found for the same radical in polycrystalline or amorphous matrices ranging from 300 to 500 meV. The analysis of the temperature dependence of spin relaxation times resulted in an activation temperature of about 3 K, assigned to temperature-activated motion of the NO within the modified open C60-derived cages with coupled rotational and translational degrees of freedom in a complicated three-dimensional locking potential.

Precise Fixation of an NO Molecule inside Carbon Nanopores: A Long‐Range Electron–Nuclear Interaction

“…The energy barrier of Δ G ≠ +1.91 kcal mol −1 implies possible free rotation of the NO molecule inside 3′ . This is also supported by a series of EPR measurements reported as a couple of this paper [16] . We also examined the effect of dimerization (Figure 3 b).…”

“…This is also supported by a series of EPR measurements reported as a couple of this paper. [16] We also examined the effect of dimerization (Figure 3 b). Upon considering difference in Gibbs energies among (NO-a@3') 2 , (NO-a@3')•(NOb@3'), and (NO-b@3') 2 at the triplet states, the apparent ratio of NO-a/NO-b was estimated to be 64:36.…”

Molecular Terms of Dioxygen and Nitric Oxide

“…The total angular momentum is denoted as J = Λ + R + S. The two additional notations are unimportant in the context of this minireview. The contribution of nuclear momentum I and rotational momentum R into J are mostly omitted here since main isotope 16 O has no nuclear spin and for the 1 O 2 ( 1 ∆ g ) molecule, we will consider the ESR spectrum for the lowest rotational state R = 0. Detailed information on the terms of diatomic molecules can be found in ref.…”

“…ESR studies of dioxygen and nitrous oxide have been performed by numerous researchers [7][8][9][10][11][12][13][14][15][16][17][18], but for their practical application in analytical purposes, we need to generalize common physical backgrounds and clarify some details that have not been considered yet.…”

“…There are many ways to generate labile singlet dioxygen [9,10,[12][13][14]17,19]. Singlet O 2 ( 1 ∆g) molecule does not have spin (S = 0) but has an electronic orbital angular momentum Λ = 2 [9][10][11][12][13][14][15][16][17]. Together with the rotational angular momentum (R), they form a total angular momentum, J = Λ + R; it is quantized along the magnetic field axis with quantum number M J .…”