AI 中文总结
研究利用光学频率梳双共振光谱测量甲烷特定范围内J≥10的转动能级，通过不同跃迁测量确定多个转动能级跃迁并归属到相关数据库，新观测到一些跃迁及多条双共振线。
AI 中文摘要
天体物理学中需要高温甲烷光谱的精确模型。以往对甲烷在P6←P2多线系范围内热带跃迁的测量限于最终转动数J≤9，更高J值的理论预测未经验证。本文利用光学-光学双共振光谱，用3.3μm窄线宽泵浦激发ν₃ P(12,A₁⁽²⁾)甲烷跃迁（P2←P0），并用1.68μm附近的腔增强频率梳探测亚多普勒阶梯型（P6←P2）和V型（P4←P0）跃迁以及多普勒展宽的碰撞诱导四能级跃迁（P6←P2）。在9510至9810 cm⁻¹范围内（即P6多线系）确定了49个最终转动态J = 10 - 12的阶梯型跃迁，其中6个达到此前未实验观测到的振动态；在6590至至6900 cm⁻¹范围内（即P4多线系）观测到19个最终态J = 11 - 13的亚多普勒V型跃迁。还观测到170条多普勒展宽的四能级双共振线，其中7条是新观测到的。
英文摘要
Accurate models of high temperature methane spectra are needed in astrophysics. Previous measurements of methane hot-band transitions in the $\it{P}$6 $\leftarrow$ $\it{P}$2 polyad range have been limited to final rotational numbers of $\it{J}$ $\le$ 9, with theoretical predictions at higher $\it{J}$s remaining unvalidated. Here, we use optical-optical double resonance spectroscopy (OODR) with a 3.3 $μ$m narrow linewidth pump to excite the $ν$${_3}$ P(12, A${_1}$$^{(2)}$) methane transition ($\it{P}$2 $\leftarrow$ $\it{P}$0) and a cavity-enhanced frequency comb centered around 1.68 $μ$m to probe the sub-Doppler ladder-type ($\it{P}$6 $\leftarrow$ $\it{P}$2) and V-type ($\it{P}$4 $\leftarrow$ $\it{P}$0) transitions, as well as Doppler-broadened collision-induced four-level transitions ($\it{P}$6 $\leftarrow$ $\it{P}$2). 49 ladder-type transitions with final rotational states $\it{J}$ = 10-12 in the range of 9510 to 9810 cm$^{-1}$ (i.e., the $\it{P}$6 polyad) were assigned to effective Hamiltonian predictions and the ExoMol database, of which 6 reached vibrational states that had not been observed experimentally before. 19 sub-Doppler V-type transitions with final states $\it{J}$ = 11-13 in the range of 6590 to 6900 cm$^{-1}$ (i.e., the $\it{P}$4 polyad) were observed and assigned to the Hamiltonian and ExoMol, while only 2 of these V-type transitions could be unambiguously assigned to WKLMC and HITRAN line lists. 170 Doppler-broadened four-level double-resonance (4LDR) lines were observed, 7 of which were newly observed compared with our previous work when pumping transitions starting from the $\it{J}$ = 7 level in the ground state [Lehmann et al., J. Chem. Phys. 163, 144304 (2025)]. We could not assign these lines as they did not form combination differences with other observed 4LDR transitions.
