Laser-induced Coulomb Explosion Imaging of Alkali Dimers on Helium Nanodroplets

Abstract

Alkali dimers, ${\mathrm{Ak}}_2$, residing on the surface of He nanodroplets are doubly ionized due to multiphoton absorption from an intense, 50-fs laser pulse leading to fragmentation into a pair of alkali cations. Based on the measured kinetic energy distributions, $P(E_{\text{kin}})$, of the ${\mathrm{Ak}}^{+}$ fragment ions, we retrieve the distribution of internuclear distances, $P(R)$, via the ${\mathrm{Ak}}_2^{2+}$ potential curve. Results are obtained for ${\mathrm{Na}}_2$, ${\mathrm{K}}_2$, ${\mathrm{Rb}}_2$, and ${\mathrm{Cs}}_2$ in both the 1 ${}^1{\Sigma }_g^{+}$ ground state and in the lowest-lying triplet state 1 ${}^3{\Sigma }_u^{+}$, and for ${\mathrm{Li}}_2$ in the 1 ${}^3{\Sigma }_u^{+}$ state. For ${\mathrm{Li}}_2$, ${\mathrm{K}}_2$, and ${\mathrm{Rb}}_2$, the center of the measured $P(R)$'s is close to the center of the wave function, $\Psi (R)$, of the vibrational ground state in the 1 ${}^1{\Sigma }_g^{+}$ and 1 ${}^3{\Sigma }_u^{+}$ states, whereas for ${\mathrm{Na}}_2$ and ${\mathrm{Cs}}_2$ small shifts are observed. For all the ${\mathrm{Ak}}_2$, the width of the measured $P(R)$ is broader than $|\Psi (R){|}^2$ by a factor of 2-4. We discuss that resonance effects in the multiphoton ionization and interaction of the ${\mathrm{Ak}}^{+}$ ion with the He droplet give rise to the observed deviations of $P(R)$ from $|\Psi (R){|}^2$. Despite these deviations, we deem that timed Coulomb explosion will allow imaging of vibrational wave packets in alkali dimers on He droplets surfaces.

10 pages, 6 figures

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Cited by in corpus (3)

• Nonadiabatic Laser-Induced Alignment Dynamics of Molecules on a Surface
• Time-resolved Coulomb explosion imaging of vibrational wave packets in alkali dimers on helium nanodroplets
• Ultrafast photodissociation dynamics of dichloromethane on three-dimensional potential energy surfaces and its Coulomb explosion signature