High-Harmonic Generation (HHG) spectra of randomly aligned bromoform (CHBr₃) molecules have been experimentally measured and theoretically simulated at various laser pulse intensities. From the experiments, we obtained a significant number of harmonics that goes beyond the cutoff limit predicted by the three-step model (3SM) with ionization from HOMO. To interpret the experiment, we resorted to real-time time-dependent configuration interaction with single excitations. We found that electronic bound states provide an appreciable contribution to the harmonics. More in detail, we analyzed the electron dynamics by decomposing the HHG signal in terms of single molecular-orbital contributions, to explain the appearance of harmonics around 20–30 eV beyond the expected cutoff due to HOMO. HHG spectra can be therefore explained by considering the contribution at high energy of HOMO–6 and HOMO–9, thus indicating a complex multiple-orbital strong-field dynamics. However, even though the presence of the bromoform cation should be not enough to produce such a signal, we could not exclude a priori that the origin of harmonics in the H29–H45 to be due to the cation, which has more energetic ionization channels.

中文翻译：

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气相三溴甲烷的高次谐波发生光谱

_{随机排列的三溴甲烷 (CHBr 3} ) 分子的高次谐波产生 (HHG) 光谱已在不同激光脉冲强度下进行了实验测量和理论模拟。从实验中，我们获得了大量谐波，这些谐波超出了 HOMO 电离三步模型 (3SM) 预测的截止极限。为了解释实验，我们采用了单次激励的实时依赖配置交互。我们发现电子束缚态对谐波有显着的贡献。更详细地说，我们通过根据单分子轨道贡献分解 HHG 信号来分析电子动力学，以解释由于 HOMO 导致超出预期截止值 20-30 eV 左右的谐波的出现。因此，HHG 光谱可以通过考虑 HOMO-6 和 HOMO-9 在高能量下的贡献来解释，从而表明复杂的多轨道强场动力学。然而，即使溴仿阳离子的存在不足以产生这样的信号，我们也不能先验地排除 H29-H45 中谐波的起源是由于具有更高能电离通道的阳离子。