arXiv subjects

Chuangang Ning

Publications and source records attributed to Chuangang Ning.

6 recordsLinked to original sources

arXiv2026

Correct Asymptotic Wavefunctions for Calculating Photoelectron Angular Distributions of O2- and NO-

The ab initio calculation of photoelectron angular distributions (PADs) for negative ions remains a significant theoretical challenge. In this work, we report a joint experimental and theoretical investigation of PADs for a series of molecular anions with varying polarities, including the nonpolar O2-, the weakly polar NO-, and the strongly polar AsO- and SbO-. To accurately describe the long-range electronic wavefunctions -- where photodetachment contributes most strongly -- we modified the standard Gaussian-type orbitals (GTOs) by augmenting them with a correct exponential Slater-tail basis set (~e^(-{\xi}r)). This simple yet effective approach significantly improves the agreement between the experimental and theoretical PADs for O2- and NO-. However, notable discrepancies persist for NO- for transitions to the v = 0 and v = 1 vibrational levels of neutral NO even after this correction. Given that our methodology successfully reproduced PADs for strongly polar anions (e.g., AsO- and SbO-), these residual discrepancies are unlikely to stem from "exit-channel scattering" induced by long-range dipole fields. Instead, we tentatively attribute the failure for NO- to the breakdown of the Born-Oppenheimer approximation or the frozen orbital approximation, arising from the extremely weak binding of the excess electron.

physics.atom-ph↗

arXiv2025

Evaluation of Quantum Offset in Velocity Imaging-Based Electron Spectrometry

Velocity-map imaging of electrons is a pivotal technique in chemical physics. A recent study reported a quantum offset as large as 0.2 cm-1 in velocity imaging-based electron spectrometry [Phys. Rev. Lett. 134, 043001 (2025)]. In this work, we assess the existence this offset through a combination of simulations and experiments. Our simulations reveal that the velocity imaging results reconstructed using the maximum entropy velocity Legendre reconstruction (MEVELER) method exhibit no such offset. Furthermore, experimental measurements of the electron affinity of oxygen conducted at various imaging voltages show no discernible offset attributable to the electric field in the photodetachment region. Therefore, we conclude that there is no evidence for the claimed quantum offset in properly analyzed velocity imaging-based electron spectrometry.

physics.atom-ph↗

arXiv2025

Revisiting the electron affinity of selenium

The electron affinity (EA) of atomic selenium, previously established as 16,297.276(9) cm-1 based on the laser photodetachment microscopy (LPM) measurements in 2012, exhibited a significant deviation from other earlier experimental values, yet it remained the accepted reference standard for over a decade. In this letter, we re-examined the EA of Se using the slow-electron velocity-map imaging method and revealed a substantial deviation in the LPM result. Measurements for the different isotopes of Se and the energy-level splitting of the neutral Se atom's 3P2 - 3P1 further verified the accuracy and robustness of our SEVI method. Based on these experimental evidences, we recommended a revised EA(Se) value of 16,297.78(4) cm-1, which is in excellent agreement with the previous laser photodetachment threshold (LPT) experimental results.

physics.atom-ph↗

arXiv2024

Energy Levels and Transition Rates of Laser-Cooling Candidate Th^-

The energy levels and transition rates of promising laser-cooling candidate thorium anion Th^- have been experimentally obtained in the current work. Three new excited states between the bound-bound electric dipole (E1) transition of Th^- are observed now, and their energy levels are determined to be 1,847(13), 3,166.8(59) and 3,666(12) cm^{-1}, respectively. Meanwhile, the lifetime of the upper state of that E1 transition is experimentally determined to be 30(2) microseconds, about 3 times shorter than the previous calculated result 86 microseconds, which makes Th^- the most promising candidate for laser cooling of negative ions. Furthermore, the lifetimes of two other short-lived odd-parity excited states of Th^- are also measured to be 59(4) and 53(3)microseconds, respectively.

physics.atom-ph↗

arXiv2019

Observation of Electric-Dipole Transitions in the Laser-Cooling Candidate Th$^-$

Despite the fact that the laser cooling method is a well-established technique to obtain ultra-cold neutral atoms and atomic cations, it has so far never been applied to atomic anions due to the lack of suitable electric-dipole transitions. Efforts of more than a decade currently has La$^-$ as the only promising candidate for laser cooling. Our previous work [Tang et al., Phys. Rev. Lett. 123, 203002(2019)] showed that Th$^-$ is also a potential candidate. Here we report on a combination of experimental and theoretical studies to determine the relevant transition frequencies, transition rates, and branching ratios in Th$^-$. The resonant frequency of the laser cooling transition is determined to be $ν/c$ = 4118.0 (10) cm$^{-1}$. The transition rate is calculated as A=1.17x10^4 s$^{-1}$. The branching fraction to dark states is very small, 1.47x10$^{-10}$, thus this represents an ideal closed cycle for laser cooling. Since Th has zero nuclear spin, it is an excellent candidate to be used to sympathetically cool antiprotons in a Penning trap.

physics.atom-ph↗

arXiv2016

A simple setup to measure muon lifetime and electron energy spectrum of muon decay and its Monte Carlo simulation

We designed a simple setup to measure the muon lifetime and the electron energy spectra of muon decay. A low cost coincidental circuit was designed to select the signals of muon decay events detected by a plastic scintillator detector. It triggered a digital oscilloscope to record the signals of muon decay events for measuring the muon lifetime and electron energy spectrum. A Landau-distribution energy loss method was introduced to conduct the energy calibration of the system. The experimental results were well reproduced by the Monte Carlo simulation. The software and hardware of the system are completely open to students, thus more helpful for instruction and motivation.

physics.ins-det↗