Kelleher Patrick J, Johnson Christopher J, Fournier Joseph A, Johnson Mark A, McCoy Anne B
†Sterling Chemistry Laboratory, Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, United States.
‡Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210, United States.
J Phys Chem A. 2015 May 7;119(18):4170-6. doi: 10.1021/acs.jpca.5b03114. Epub 2015 Apr 24.
To explore the extent of the molecular cation perturbation induced by complexation with He atoms required for the application of cryogenic ion vibrational predissociation (CIVP) spectroscopy, we compare the spectra of a bare NH4(+)(H2O) ion (obtained using infrared multiple photon dissociation (IRMPD)) with the one-photon CIVP spectra of the NH4(+)(H2O)·He1-3 clusters. Not only are the vibrational band origins minimally perturbed, but the rotational fine structures on the NH and OH asymmetric stretching vibrations, which arise from the free internal rotation of the -OH2 and -NH3 groups, also remain intact in the adducts. To establish the location and the quantum mechanical delocalization of the He atoms, we carried out diffusion Monte Carlo (DMC) calculations of the vibrational zero point wave function, which indicate that the barriers between the three equivalent minima for the He attachment are so small that the He atom wave function is delocalized over the entire -NH3 rotor, effectively restoring C3 symmetry for the embedded -NH3 group.
为了探索与氦原子络合所引起的分子阳离子扰动程度，这是低温离子振动预解离（CIVP）光谱应用所必需的，我们将裸NH4(+)(H2O)离子的光谱（通过红外多光子解离（IRMPD）获得）与NH4(+)(H2O)·He1-3团簇的单光子CIVP光谱进行了比较。不仅振动带起源受到的扰动极小，而且由-OH2和-NH3基团的自由内旋转产生的NH和OH不对称伸缩振动上的转动精细结构在加合物中也保持完整。为了确定氦原子的位置和量子力学离域，我们对振动零点波函数进行了扩散蒙特卡罗（DMC）计算，结果表明氦原子附着的三个等效极小值之间的势垒非常小，以至于氦原子波函数在整个-NH3转子上离域，有效地恢复了嵌入的-NH3基团的C3对称性。
