## 1 Introduction  
Developments in the field of trapped particles have enabled the exploration of dynamical processes under the action of diverse short-range and long-range interactions. A detailed characterization of the spatial distribution and energy distribution of these trapped particles is imperative to investigate phenomena in ultracold chemistry [1; 2; 3; 4; 5; 6; 7; 8], astrophysics [9], as well as astrochemistry [10], including the formation and evolution of the interstellar medium (ISM) [11; 12; 13; 14; 15]. For charged particles trapped in multipole ion traps, the measurement of temperature-dependent ion mobility and rate coefficients is one of the key methods to characterize the temperature of the ions [16]. With advances in the application of electrostatic lenses, another method called velocity map imaging became feasible such that ions with same initial velocity in the trap could be mapped onto the same point on the detector [17]. Similar to atoms, the phase space distribution of the trapped ions with closed optical transitions can also be characterized via Doppler-spectroscopy [18; 19; 20; 21; 22; 23]. However, this is limited to only a number of atomic cations. In case of molecular anions, a detailed characterization for the internal thermometry via photodetachment techniques exists [24]. However, due to the rethermalization of the ions with the black-body radiation, the temperature of ions in the external and internal degrees of freedom are not necessarily the same. Recent work [25] measured the translational temperature of hydroxyl (OH\({}^{-}\)) anions via the Doppler width of an overtone transition, but this method is time-intensive and requires an exact knowledge of the overtone transition frequency.  
In this work, we put forward a versatile tool to characterize the translational temperature of ions trapped in a multipole ion trap by mapping the ions' time-of-flight (TOF) to the detector. Here, we describe an octupole radio frequency (rf) wire trap in a Hybrid Atom-Ion trap (HAI-trap) setup. We start by detailing the experimental setup and the ion trap assembly in Section 2 and Section 3, respectively. The current setup is an improved version of the earlier design described in [26]. Following the description of the trap, we investigate the potential landscape created by a multipole wire trap and traps with ideal cylindrical or hyperbolic rods in Section 4. We further compare the influence of different trap geometries on the final energy distribution of the trapped ions after interaction with a buffer gas. Then, in Section 5, we extend our investigations to the HAI-trap setup, where the 3-dimensional (3D) model of the system is used to simulate potential landscape in the trap, including surface charges that accumulate on the plastic components of the trap. The ion distributions obtained via the simulated potentials are compared with the measured ion distributions obtained via photodetachment tomography [27; 28]. It is shown that the spatial energy distribution of ions in the trap can be mapped onto the ions' time-of-flight to the detector, including the effect of multiple regions of potential minima that arise in multipole ion traps (with the pole order \(>2\)). Independent of the trapped ionic species, this technique is time-efficient and can be applied to any system without relying on the existence of suitable transitions for determining the ions' motional temperature.