Improved line list of 12CH4 in the 4100-4300 cm-1 region

Four spectra of methane in natural isotopic abundance in the 4100-4300 cm-1 region were recorded by using a Fourier transform spectrometer in Reims, France at long paths (202 m, 602 m, 1604 m and 1804 m) and different pressures. Additional spectra of 12CH4 covering the same region were obtained at 100-123 K for different pressures, 93 m path length at Synchrotron SOLEIL in Paris for different pressures and were used to measure low-J lines. Spectra of 12CH4 and 13CH4 obtained at 80 K at JPL were used for additional frequency calibrations. Line positions and intensities were retrieved by non-linear least-squares curve-fitting procedures and analyzed using effective Hamiltonian and effective dipole transition moment models. A new measured line list contains positions and intensities for 12274 features. Quantum assignments were made for more than 11472 new transitions, which represent ~99% of the integrated line intensity observed in this region. Some of 4592 hot band transitions for (Dyad – Tetradecad) system were assigned. The resulting list of lines is significantly more accurate than previous empirical compilations. All assigned 6972 line positions were fitted to RMS standard deviations of 0.0015 cm-1. The sum of the observed intensities between 4100 and 4300 cm-1 falls within 5% of the predicted value from ab initio variational calculations reported in the TheoReTS database (http://theorets.univ-reims.fr ; http://theorets.tsu.ru).

本研究于法国兰斯（Reims）采用傅里叶变换光谱仪（Fourier transform spectrometer），在不同长光程（202 m、602 m、1604 m及1804 m）与压力条件下，采集了4组天然同位素丰度甲烷在4100~4300 cm⁻¹波数区间的光谱。此外，本研究在巴黎的索莱欧同步辐射装置（Synchrotron SOLEIL）中，于100~123 K、不同压力及93 m光程条件下，采集了覆盖同一波数区间的12CH4光谱，该光谱用于测量低转动量子数J的谱线。此外，在喷气推进实验室（Jet Propulsion Laboratory, JPL）中于80 K下采集的12CH4与13CH4光谱，被用于额外的频率校准工作。研究人员通过非线性最小二乘曲线拟合程序提取谱线位置与强度，并采用有效哈密顿量（effective Hamiltonian）及有效偶极跃迁矩模型开展分析。本研究构建的新实测谱线列表包含12274个谱峰的位置与强度信息。已对该区间内超过11472条新跃迁谱线完成量子归属，其积分总强度占该区间观测总积分强度的约99%。已对（二重态-十四重态）体系的4592条热谱带跃迁中的部分谱线完成归属。最终得到的谱线列表相较于此前的经验汇编结果，精度有显著提升。所有已归属的6972条谱线位置的拟合均方根（root mean square, RMS）标准偏差为0.0015 cm⁻¹。4100~4300 cm⁻¹区间内观测强度的总和，与TheoReTS数据库（http://theorets.univ-reims.fr；http://theorets.tsu.ru）中报道的从头算变分计算预测值的偏差在5%以内。