Structural relaxation dynamics of electronically excited XeArN clusters

In this article we explore the structural, dynamic, and spectroscopic implications of large local configurational changes in electronically excited ${\mathrm{Xe}}^{\mathrm{*}}{\mathrm{Ar}}_N$ $\text{(N=12,54,146,199)}$ heteroclusters, where the ${\mathrm{Xe}}^{*}$ $\mathrm{[\equiv }\mathrm{Xe}{(}^3{P}_1\mathrm{)]}$ atom is excited to the lowest dipole-allowed extravalence Rydberg excitation. The ultrafast femtosecond and picosecond dynamics driven by the short-range repulsive interaction between the vertically excited ${\mathrm{Xe}}^{*}$ Rydberg and the cluster Ar atoms was studied by molecular dynamics simulations. From the analysis of the time dependence of the structural parameters for site-specific Xe excitations in medium-sized $\text{(N=54)}$ and large ($\text{N=146,199)}$ clusters, two general configurational relaxation phenomena were established: a “bubble” formation (i.e., a large configurational dilation around ${\mathrm{Xe}}^{*}$ ) for Xe interior sites and a “spring” formation (i.e., the stretching of ${\mathrm{Xe}}^{*}$ outside the cluster) for Xe surface sites. General Xe site-specific features of both bubble and spring formation involve ultrashort (Gaussian) energy transfer to the cluster $\text{(∼50–100\hspace{0.17em}}\mathrm{fs}$ characteristic times ${\tau }_{\mathrm{ET}}$ ) inducing configurational relaxation, which manifests a multimodal time solution. The initial (Gaussian) temporal mode ($\text{∼150–300\hspace{0.17em}}\mathrm{fs}$ characteristic times ${\tau }_0{\mathrm{>\tau }}_{\mathrm{ET}}$ ) is followed by an exponential mode (ps lifetime ${\tau }_1$ ), with subsequent impact induced, damped vibrational coherence effects with frequencies ${\mathrm{(\omega }}_2{\mathrm{,\omega }}_3\mathrm{),}$ and exponential decay (ps lifetimes ${\tau }_2{\mathrm{,\tau }}_3$ ). The bubble formation for the central site of ${\mathrm{Xe}}^{\mathrm{*}}{\mathrm{Ar}}_{\mathrm{146}}$ or ${\mathrm{Xe}}^{\mathrm{*}}{\mathrm{Ar}}_{\mathrm{54}}$ is induced by energy transfer of ${\tau }_{\mathrm{ET}}\mathrm{\cong 60\hspace{0.17em}fs}$ followed by subsequent multimodal dilation with ${\tau }_0\text{≅170\hspace{0.17em}}\mathrm{fs}$ and ${\tau }_1\text{≅2\hspace{0.17em}}\mathrm{ps},$ and a subsequent expansion with coherent motion of vibrational wave packets with ${\omega }_2{\mathrm{,\omega }}_3\text{≅20,}$ $\text{40\hspace{0.17em}}{\mathrm{cm}}^{\mathrm{-1}}$ and ${\tau }_2{\mathrm{,\tau }}_3\text{≅2,}$ 6 ps. The bubble reaches an equilibrium configuration after $\text{∼10\hspace{0.17em}}\mathrm{ps}$ with asymptotic spatial expansion of ${\mathrm{\Delta R}}_b^{*}\text{=0.7–0.8\hspace{0.17em}Å.}$ The spring formation for an exterior surface site of ${\mathrm{Xe}}^{\mathrm{*}}{\mathrm{Ar}}_{\mathrm{146}}$ is ${\tau }_{\mathrm{ET}}\mathrm{\cong 80\hspace{0.17em}fs}$ and