Molecular-ion trap-depletion spectroscopy of BaCl${}^{+}$

We demonstrate a simple technique for molecular-ion spectroscopy. BaCl${}^{+}$ molecular ions are trapped in a linear Paul trap in the presence of a room-temperature He buffer gas and photodissociated by driving an electronic transition from the ground $X\hspace{0.5em}{}^1{\Sigma }^{+}$ state to the repulsive wall of the $A\hspace{0.5em}{}^1\Pi$ state. The photodissociation spectrum is recorded by monitoring the induced trap loss of BaCl${}^{+}$ ions as a function of excitation wavelength. Accurate molecular potentials and spectroscopic constants are determined. A comparison of the theoretical photodissociation cross sections with the measurements shows excellent agreement. This study represents an important step toward the production of ultracold ground-state molecular ions.

Figure 1

Schematic of the depletion spectroscopy apparatus based on a linear Paul trap.

Figure 2

Effect of the PDL light on BaCl${}^{+}$ and Yb${}^{+}$. Each data point represents the mean of eight measurements with error bars reflecting the corresponding standard error. A single exponential decay curve is fit to the BaCl${}^{+}$ data to calculate the photodissociation rate.

Figure 3

Measured BaCl${}^{+}$ photodissociation rate versus PDL pulse energy. The linear dependence is indicative of a one-photon photodissociation process. Each point is the result of a decay rate fit shown in Fig. 2 with error bars reflecting the fitting error.

Figure 4

Experimental and theoretical cross-section values for the $A$${}^1\Pi \leftarrow$ $X$${}^1{\Sigma }^{+}$ transition as functions of the photon energy. Each data point is associated with a set of data similar to that in Fig. 3. The theoretical curves are thermally averaged for temperatures of 300 K and 1 mK.

Figure 5

Potential energy curves of the BaCl${}^{+}$ molecular ion as a function of the internuclear separation $R$. Solid, labeled curves indicate the potentials that are involved in the photodissociation scheme. Other ${}^1{\Sigma }^{+}$ (${}^1\Pi$) potentials are shown by dashed or dash-dotted lines. The vertical arrow indicates the $A$${}^1\Pi \leftarrow$ $X$${}^1{\Sigma }^{+}$ single-photon photodissociation transition.