Photoelectron-Photofragment Coincidence Spectroscopy With Ions Prepared in a Cryogenic Octopole Accumulation Trap: Collisional Excitation and Buffer Gas Cooling

Abstract

A cryogenic octopole accumulation trap (COAT) has been coupled to a photoelectron-photofragment coincidence (PPC) spectrometer allowing for improved control over anion vibrational excitation. The anions are heated and cooled via collisions with buffer gas <17 K. Shorter trapping times (500 μs) prevent thermalization and result in anions with high internal excitation while longer trapping times (80 ms) at cryogenic temperatures thermalize the ions to the temperature of the buffer gas. The capabilities of the COAT are demonstrated using PPC spectroscopy of at 388 nm (E hν = 3.20 eV). Cooling the precursor anions with COAT resulted in the elimination of the autodetachment of vibrationally excited produced by the photodissociation + hν → O + (v ≥ 4). Under heating conditions, a lower limit temperature for the anions was determined to be 1,500 K through Franck-Condon simulations of the photodetachment spectrum of , considering a significant fraction of the ions undergo photodissociation in competition with photodetachment. The ability to cool or heat ions by varying ion injection and trapping duration in COAT provides a new flexibility for studying the spectroscopy of cold ions as well as thermally activated processes.

Photoelectron photofragment coincidence spectroscopy of carboxylates

“…This will allow the decarboxylation dynamics of vibrationally cold carboxylates to be studied in a kinematically complete manner, with the aim to probe the effect of vibrational excitation on the decarboxylation dynamics and reduce spectral congestion. 25,43 These studies will also be extended to other biologically and atmospherically relevant carboxylates such as citrate and pyruvate. The implementation of the LINAC on the high beam energy PPC spectrometer has increased the mass difference between the parent anion and the neutral fragment that can be successfully studied by PPC spectroscopy, by increasing the detectability of the light fragments.…”