Stockett Mark H, Bull James N, Schmidt Henning T, Zettergren Henning
Department of Physics, Stockholm University, Stockholm, Sweden.
School of Chemistry, University of East Anglia, Norwich, UK.
Phys Chem Chem Phys. 2022 May 18;24(19):12002-12010. doi: 10.1039/d2cp00490a.
We report measurements of the statistical vibrational autodetachment (VAD, also called thermionic emission) and radiative cooling rates of isolated -benzoquinone (BQ, CHO) radical anions using the cryogenic electrostatic ion storage ring facility DESIREE. The results are interpreted using master equation simulations with rate coefficients calculated using statistical detailed balance theory. The VAD rate is determined by measuring the time-dependent yield of neutral BQ due to spontaneous electron emission from a highly-excited ensemble of anions formed in an electron-attachment ion source. Competition with radiative cooling quenches the VAD rate after a critical time of = 11.00(5) ms. Master equation simulations which reproduce the VAD yield provide an estimate of the initial effective vibrational temperature of the ions of 1100(20) K, and provide insight into the anion formation scenario. A second measurement of the radiative cooling rate of BQ stored for up to 0.5 s was achieved using time-dependent photodetachment action spectroscopy across the A ← B and B ← B transitions. The rate at which hot-band contributions fade from the action spectrum is quantified by non-negative matrix factorisation. This is found to be commensurate with the average vibrational energy extracted from the simulations, with 1/ lifetimes of 0.16(3) s and 0.1602(7) s, respectively. Implications for astrochemistry are discussed.
我们报告了使用低温静电离子储存环装置DESIREE对孤立的对苯醌（BQ，C₆H₄O₂）自由基阴离子的统计振动自脱附（VAD，也称为热电子发射）和辐射冷却速率的测量结果。使用主方程模拟对结果进行解释，其中速率系数是根据统计详细平衡理论计算得出的。VAD速率是通过测量由于电子附着离子源中形成的高激发阴离子集合体的自发电子发射而导致的中性BQ随时间变化的产率来确定的。在临界时间τ = 11.00(5) ms后，与辐射冷却的竞争会淬灭VAD速率。再现VAD产率的主方程模拟给出了离子初始有效振动温度的估计值为1100(20) K，并深入了解了阴离子的形成情况。通过对A←B和B←B跃迁进行随时间变化的光脱附作用光谱，实现了对储存长达0.5 s的BQ辐射冷却速率的第二次测量。通过非负矩阵分解对热带贡献从作用光谱中衰减的速率进行了量化。发现这与从模拟中提取的平均振动能量相当，其1/τ寿命分别为0.16(3) s和0.1602(7) s。讨论了对天体化学的影响。
