Threshold photodetachment spectroscopy has been performed on the molecular anion CN − at both 16(1) K and 295(2) K in a 22-pole ion trap and at 295(2) K from a pulsed ion beam. The spectra show a typical energy dependence of the detachment cross section yielding a determination of the electron affinity of CN to greater precision than has previously been known at 31 163(16) cm −1 [3.864(2) eV]. Allowed s-wave detachment is observed for CN − , but the dependence of the photodetachment cross section near the threshold is perturbed by the long-range interaction between the permanent dipole moment of CN and the outgoing electron. Furthermore, we observe a temperature dependence of the cross section near the threshold, which we attribute to a reduction of the effective permanent dipole due to higher rotational excitation at higher temperatures.

Laser initiated reactions in N2O clusters studied by time-sliced ion velocity imaging technique J. Chem. Phys. 139, 044307 (2013) We present a new photo-fragment imaging spectrometer, which employs a movable repeller in a single field imaging geometry. This innovation offers two principal advantages. First, the optimal fields for velocity mapping can easily be achieved even using a large molecular beam diameter (5 mm); the velocity resolution (better than 1%) is sufficient to easily resolve photo-electron recoil in (2 + 1) resonant enhanced multiphoton ionization of N 2 photoproducts from N 2 O or from molecular beam cooled N 2 . Second, rapid changes between spatial imaging, velocity mapping, and slice imaging are straightforward. We demonstrate this technique's utility in a re-investigation of the photodissociation of N 2 O. Using a hot nozzle, we observe slice images that strongly depend on nozzle temperature. Our data indicate that in our hot nozzle expansion, only pure bending vibrations -(0, v 2 , 0) -are populated, as vibrational excitation in pure stretching or bend-stretch combination modes are quenched via collisional near-resonant V-V energy transfer to the nearly degenerate bending states. We derive vibrationally state resolved absolute absorption cross-sections for (0, v 2 ≤ 7, 0). These results agree well with previous work at lower values of v 2 , both experimental and theoretical. The dissociation energy of N 2 O with respect to the O( 1 D) + N 2 1 + g asymptote was determined to be 3.65 ± 0.02 eV.

We report the first experimental evidence of spontaneous electron emission from a homonuclear dimer anion through direct measurements of Ag − 2 → Ag 2 + e − decays on milliseconds and seconds time scales. This observation is very surprising as there is no avoided crossing between adiabatic energy curves to mediate such a process. The process is weak but yet dominates the decay signal after 100 ms when ensembles of internally hot Ag − 2 ions are stored in the cryogenic ion-beam storage ring, DESIREE, for 10 seconds. The electron emission process is associated with an instantaneous, very large, reduction of the vibrational energy of the dimer system. This represents a dramatic deviation from a Born-Oppenheimer description of dimer dynamics.In the Born-Oppenheimer approximation for molecules, the electronic and nuclear degrees of freedom are treated separately [1]. This is the basis for representing molecular quantum states as products of electronic and vibrational-rotational wavefunctions. Strictly within such a description, no instantaneous transfer of energy between electronic and nuclear degrees of freedom is possible. For complex systems, rapid transfers of energy between electronic and nuclear degrees of freedom are nevertheless common. The energy transfer may happen when such systems are photoexcited and evolve from an electronically excited potential energy surface via one or more conical intersections to the ground state [2]. The reverse process-inverse internal conversion-where a vibrationally hot complex system in the electronic ground state converts vibrational energy to electronic excitations is possible as well and may lead to recurrent fluorescence processes [3][4][5][6]. Rapid transfer of energy between the electronic and nuclear degrees of freedom is also expected for most small metal cluster anions [7][8][9]. These processes are often very fast. Typically, they occur on picosecond timescales at avoided crossings or conical intersections with small separations between potential energy curves or surfaces. Recently, electron emission from excited sulfur hexafluoride anions was ascribed to a crossing of the anion and neutral potential energy surfaces [10], yielding a strong coupling to the electron continuum states.For a range of homonuclear metal dimer anions such as Cu − 2 , Ag − 2 , and Au − 2 , the situation is fundamentally