Calibrations are given to extract orientation order parameters from pseudo-powder electron paramagnetic resonance line shapes of 14N-nitroxide spin labels undergoing slow rotational diffusion. The nitroxide z-axis is assumed parallel to the long molecular axis. Stochastic-Liouville simulations of slow-motion 9.4-GHz spectra for molecular ordering with a Maier–Saupe orientation potential reveal a linear dependence of the splittings, $$2A_{\hbox{max} }$$2Amax and $$2A_{\hbox{min} }$$2Amin, of the outer and inner peaks on order parameter $$S_{zz}$$Szz that depends on the diffusion coefficient $$D_{{{\text{R}} \bot }}$$DR⊥ which characterizes fluctuations of the long molecular axis. This results in empirical expressions for order parameter and isotropic hyperfine coupling: $$S_{zz} = s_{1} \times \left( {A_{\hbox{max} } - A_{\hbox{min} } } \right) - s_{o}$$Szz=s1×Amax-Amin-so and $$a_{o}^{{}} = \tfrac{1}{3}\left( {f_{\hbox{max} } A_{\hbox{max} } + f_{\hbox{min} } A_{\hbox{min} } } \right) + \delta a_{o}$$ao=13fmaxAmax+fminAmin+δao, respectively. Values of the calibration constants $$s_{1}$$s1, $$s_{\text{o}}$$so, $$f_{\hbox{max} }$$fmax, $$f_{\hbox{min} }$$fmin and $$\delta a_{o}$$δao are given for different values of $$D_{{{\text{R}} \bot }}$$DR⊥ in fast and slow motional regimes. The calibrations are relatively insensitive to anisotropy of rotational diffusion $$(D_{{{\text{R}}//}} \ge D_{{{\text{R}} \bot }} )$$(DR//≥DR⊥), and corrections are less significant for the isotropic hyperfine coupling than for the order parameter.

中文翻译：

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慢动作的自旋标签顺序参数校准

给出校准以从经历缓慢旋转扩散的 14N-氮氧化物自旋标记的伪粉末电子顺磁共振线形状中提取取向顺序参数。假定氮氧化物 z 轴平行于分子长轴。具有 Maier-Saupe 取向势的分子排序慢动 9.4-GHz 光谱的随机刘维尔模拟揭示了分裂的线性相关性，$$2A_{\hbox{max} }$$2Amax 和 $$2A_{\hbox {min} }$$2Amin，顺序参数 $$S_{zz}$$Szz 的外峰和内峰，取决于扩散系数 $$D_{{{\text{R}} \bot }}$$ DR⊥ 表征分子长轴的波动。这导致阶参数和各向同性超精细耦合的经验表达式：$$S_{zz} = s_{1} \times \left( {A_{\hbox{max} } - A_{\hbox{min} } } \right) - s_{o}$$Szz=s1×Amax -Amin-so 和 $$a_{o}^{{}} = \tfrac{1}{3}\left( {f_{\hbox{max} } A_{\hbox{max} } + f_{\hbox {min} } A_{\hbox{min} } } \right) + \delta a_{o}$$ao=13fmaxAmax+fminAmin+δao 分别。校准常数值 $$s_{1}$$s1, $$s_{\text{o}}$$so, $$f_{\hbox{max} }$$fmax, $$f_{\hbox{ min} }$$fmin 和 $$\delta a_{o}$$δao 是针对不同的 $$D_{{{\text{R}} \bot }}$$DR⊥ 在快慢运动状态下给出的. 校准对旋转扩散的各向异性 $$(D_{{{\text{R}}//}} \ge D_{{{\text{R}} \bot }} )$$(DR// ≥DR⊥)，并且对各向同性超精细耦合的校正不如顺序参数重要。