Rotational coherences in O$_2^+$ following strong-field ionization
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| Format: | Preprint |
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2025
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| _version_ | 1866908441942949888 |
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| author | Lam, Huynh Van Sa Wangjam, Tomthin Nganba Kumarappan, Vinod |
| author_facet | Lam, Huynh Van Sa Wangjam, Tomthin Nganba Kumarappan, Vinod |
| contents | We investigate the wave packet that remains bound in the ground and excited cationic states of oxygen after strong-field ionization by an intense 800-nm pulse. Much weaker probe pulses (800 or 264 nm) are used to dissociate these still-bound cations. The momentum distribution of O$^+$ is measured as a function of pump-probe delay and Fourier-transformed to obtain kinetic-energy-dependent and rotational-state-resolved quantum beat spectra. The sub-cm$^{-1}$ resolution of the Fourier transform allows unambiguous identification of the electronic, vibrational, and rotational states populated by the pump and then dissociated by the probe. Although strong-field ionization is expected to populate the lower-lying $X^2Π_g$ and $a^4Π_u$ states more effectively than the $b^4Σ^{-}_g$ state, a wave packet in the $X^2Π_g$ state is seen only with the 264-nm probe and only weak signatures of the $a^4Π_u$ states are found with either probe. The experiment confirms the role of the resonant coupling between the $b^4Σ^{-}_g$ and $a^4Π_u$ states by the 800 nm pulses [Xue \textit{et al.}, Phys. Rev. A 97, 043409 (2018)] and reveals the importance of rovibrational excitation in determining the momentum distribution of the O$^+$ fragments. The strong $X^2Π_g$ state contribution observed with the 264-nm probe also shows the importance of resonant coupling in the probe pulse. The sub-cm$^{-1}$ resolution also resolves spin-orbit splitting in both the $X^2Π_g$ and $a^4Π_u$ state wave packets. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2507_06680 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Rotational coherences in O$_2^+$ following strong-field ionization Lam, Huynh Van Sa Wangjam, Tomthin Nganba Kumarappan, Vinod Atomic Physics Atomic and Molecular Clusters Optics We investigate the wave packet that remains bound in the ground and excited cationic states of oxygen after strong-field ionization by an intense 800-nm pulse. Much weaker probe pulses (800 or 264 nm) are used to dissociate these still-bound cations. The momentum distribution of O$^+$ is measured as a function of pump-probe delay and Fourier-transformed to obtain kinetic-energy-dependent and rotational-state-resolved quantum beat spectra. The sub-cm$^{-1}$ resolution of the Fourier transform allows unambiguous identification of the electronic, vibrational, and rotational states populated by the pump and then dissociated by the probe. Although strong-field ionization is expected to populate the lower-lying $X^2Π_g$ and $a^4Π_u$ states more effectively than the $b^4Σ^{-}_g$ state, a wave packet in the $X^2Π_g$ state is seen only with the 264-nm probe and only weak signatures of the $a^4Π_u$ states are found with either probe. The experiment confirms the role of the resonant coupling between the $b^4Σ^{-}_g$ and $a^4Π_u$ states by the 800 nm pulses [Xue \textit{et al.}, Phys. Rev. A 97, 043409 (2018)] and reveals the importance of rovibrational excitation in determining the momentum distribution of the O$^+$ fragments. The strong $X^2Π_g$ state contribution observed with the 264-nm probe also shows the importance of resonant coupling in the probe pulse. The sub-cm$^{-1}$ resolution also resolves spin-orbit splitting in both the $X^2Π_g$ and $a^4Π_u$ state wave packets. |
| title | Rotational coherences in O$_2^+$ following strong-field ionization |
| topic | Atomic Physics Atomic and Molecular Clusters Optics |
| url | https://arxiv.org/abs/2507.06680 |