The ion-molecule reactions ${\mathrm{D}}_2^{+}+{\mathrm{NH}}_3$ and ${\mathrm{D}}_2^{+}+{\mathrm{ND}}_3$ are studied at low collision energies ($E_{\mathrm{coll}}$ from zero to approximately $k_B\times 50\mathrm{K}$), with the ${\mathrm{D}}_2^{+}$ ions in the ground rovibrational state and for different rotational temperatures of the ammonia molecules, using the Rydberg-Stark merged-beam approach. Two different rotational temperatures (approximately 15 K and approximately 40 K), measured by ($2+1$) resonance-enhanced multiphoton-ionization spectroscopy, are obtained by using a seeded supersonic expansion in He and a pure ammonia expansion, respectively. The experimental data reveal a strong enhancement of the rate coefficients at the lowest collision energies caused by the charge-dipole interaction. Calculations based on a rotationally adiabatic capture model accurately reproduce the observed kinetic-energy dependence of the rate coefficients. The rate coefficients increase with increasing rotational temperature of the ammonia molecules, which contradicts the expectation that rotational excitation should average the dipoles out. Moreover, these reactions exhibit a pronounced inverse kinetic isotope effect. The difference is caused by nuclear-spin-statistical factors and the smaller rotational constants and tunneling splittings in ${\mathrm{ND}}_3$.

中文翻译：

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旋转和平移能量对 0 K 附近离子分子反应速率的相反影响：D2++NH3 和 D2++ND3 反应

离子-分子反应${\mathrm{D}}_2^{+}+{\mathrm{NH}}_3$和${\mathrm{D}}_2^{+}+{\mathrm{ND}}_3$在低碰撞能量下进行研究（${乙}_{\mathrm{科尔}}$从零到大约$k_{乙}\times 50\mathrm{K}$），与${\mathrm{D}}_2^{+}$使用里德堡-斯塔克合并束方法，对处于地面旋转振动状态的离子和氨分子的不同旋转温度进行分析。两个不同的旋转温度（大约 15 K 和大约 40 K），通过 ($2+1$）共振增强多光子电离光谱，分别通过使用氦气中的种子超音速膨胀和纯氨膨胀来获得。实验数据表明，电荷-偶极子相互作用导致最低碰撞能量下速率系数的显着增强。基于旋转绝热捕获模型的计算准确地再现了观察到的速率系数的动能依赖性。速率系数随着氨分子旋转温度的增加而增加，这与旋转激发应使偶极子平均化的预期相矛盾。此外，这些反应表现出明显的逆动力学同位素效应。这种差异是由核自旋统计因素以及较小的旋转常数和隧道分裂引起的${\mathrm{ND}}_3$。