Abstract Spontaneous Raman scattering from nitrogen is well-suited for temperature measurements in combustion experiments, especially at high pressure which increases the Raman signal because of the higher density in the measurement volume. In this work we investigate high density effects on the anisotropic tensor component of ro-vibrational spontaneous Raman scattering, which must be understood to obtain accurate thermometry in high pressure gases using high-fidelity Raman simulations. We measure the collision broadening for the anisotropic component of spontaneous Raman scattering from room temperature nitrogen over the pressure range 10–70 atm for three gas compositions: pure nitrogen, air, and nitrogen in argon. Line broadening coefficients inferred from these measurements were found to be 14 ± 5% larger than the corresponding broadening coefficients of the isotropic Q branch. Air broadening coefficients were found to be very similar and about 2.5% smaller than nitrogen self-broadening coefficients. Argon broadening coefficients were 25% smaller at rotational quantum number 7 and about 50% smaller at rotational quantum number 21. Additionally, we found that our unmixed line model for the O and S branches gave good fits for all pressures, which indicates that line mixing effects are not significant in the O and S branches over this range of pressures. Using indirect experimental evidence we infer that line mixing effects in the anisotropic component of the Q branch were below the threshold set by our experimental spectral resolution at pressures up to 70 atm at room temperature. Assuming that the anisotropic Q branch lines mix like the isotropic lines results in a small systematic error in the inferred temperature at flame temperatures, with the error increasing slowly with pressure. The bias can be easily removed by modeling the anisotropic spectrum separately from the isotropic spectrum. Line mixing effects should be included in the model of the isotropic part of the Raman spectrum, but can probably be neglected in the anisotropic part of the spontaneous Raman spectrum of N2 for pressures below 400 atm at flame temperatures.

中文翻译：

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自发拉曼光谱各向异性张量分量中 N2 压力展宽的测量

摘要 氮气的自发拉曼散射非常适合燃烧实验中的温度测量，特别是在高压下，由于测量体积的密度较高，拉曼信号会增加。在这项工作中，我们研究了高密度对旋转振动自发拉曼散射的各向异性张量分量的影响，必须了解这一点，才能使用高保真拉曼模拟在高压气体中获得准确的温度测量。我们测量了三种气体成分：纯氮气、空气和氩气中的氮气，在 10-70 个大气压的压力范围内，来自室温氮气的自发拉曼散射的各向异性分量的碰撞展宽。发现从这些测量中推断出的线加宽系数比各向同性 Q 分支的相应加宽系数大 14 ± 5%。发现空气展宽系数非常相似，比氮气自展宽系数小约 2.5%。氩气展宽系数在旋转量子数 7 处小 25%，在旋转量子数 21 处小约 50%。此外，我们发现我们的 O 和 S 分支的未混合线模型对所有压力都有很好的拟合，这表明线混合在这个压力范围内，O 和 S 分支的影响不显着。使用间接实验证据，我们推断 Q 分支的各向异性分量中的线混合效应低于我们的实验光谱分辨率在室温下高达 70 个大气压的压力下设置的阈值。假设各向异性 Q 支线像各向同性线一样混合会导致火焰温度下推断温度的系统误差很小，误差随压力缓慢增加。通过将各向异性光谱与各向同性光谱分开建模，可以轻松消除偏差。线混合效应应包括在拉曼光谱各向同性部分的模型中，但在火焰温度下压力低于 400 atm 时，在 N2 的自发拉曼光谱的各向异性部分中可能可以忽略不计。假设各向异性 Q 支线像各向同性线一样混合会导致火焰温度下推断温度的系统误差很小，误差随压力缓慢增加。通过将各向异性光谱与各向同性光谱分开建模，可以轻松消除偏差。线混合效应应包括在拉曼光谱各向同性部分的模型中，但在火焰温度下压力低于 400 atm 时，在 N2 的自发拉曼光谱的各向异性部分中可能可以忽略不计。假设各向异性 Q 支线像各向同性线一样混合会导致火焰温度下推断温度的系统误差很小，误差随压力缓慢增加。通过将各向异性光谱与各向同性光谱分开建模，可以轻松消除偏差。线混合效应应该包括在拉曼光谱的各向同性部分的模型中，但在火焰温度下压力低于 400 atm 的 N2 自发拉曼光谱的各向异性部分中可能可以忽略不计。