Development of a low-temperature photoelectron spectroscopy instrument using an electrospray ion source and a cryogenically controlled ion trap

Abstract

The ability to control ion temperatures is critical for gas phase spectroscopy and has been a challenge in chemical physics. A low-temperature photoelectron spectroscopy instrument has been developed for the investigation of complex anions in the gas phase, including multiply charged anions, solvated species, and biological molecules. The new apparatus consists of an electrospray ionization source, a three dimensional (3D) Paul trap for ion accumulation and cooling, a time-of-flight mass spectrometer, and a magnetic-bottle photoelectron analyzer. A key feature of the new instrument is the capability to cool and tune ion temperatures from 10 to 350 K in the 3D Paul trap, which is attached to the cold head of a closed cycle helium refrigerator. Ion cooling is accomplished in the Paul trap via collisions with a background gas and has been demonstrated by observation of complete elimination of vibrational hot bands in photoelectron spectra of various anions ranging from small molecules to complex species. Further evidence of ion cooling is shown by the observation of H2-physisorbed anions at low temperatures. Cold anions result in better resolved photoelectron spectra due to the elimination of vibrational hot bands and yield more accurate energetic and spectroscopic information. Temperature-dependent studies are made possible for weakly bonded molecular and solvated clusters, allowing thermodynamic information to be obtained.

Perspective: Electrospray photoelectron spectroscopy: From multiply-charged anions to ultracold anions

“…Four major modifications were implemented in the new ESI-PES apparatus: (1) the ESI source with more compact ion optics; (2) the cryogenically cooled Paul trap with pulsed thermalization gas and a more powerful cryostat; (3) the replacement of the magnetic-bottle PES analyzer with a high-resolution co-linear PE imaging system; and (4) the improved vacuum system by replacing all diffusion pumps with turbomolecular pumps. The time-of-flight mass spectrometer is similar to the previous design, 37,41 with the exception of the ion detector, which is now placed in front of the co-linear PE imaging lens and can be moved out of the ion path during PE imaging experiments (Fig. 1).…”

“…Consequently, significant thermal broadening was observed, limiting the PES resolution and the accuracy of the measured electron binding energies. A second-generation ESI-PES apparatus was developed, 41 which featured a cryogenically cooled Paul trap. This advance not only allowed high-resolution PES data to be obtained by eliminating vibrational hot bands [42][43][44][45] but has also allowed temperature-dependent phenomena to be studied.…”

“…41 Hence, the full benefits of actively cooling the anions cannot be fully capitalized due to the limited resolution of the magnetic-bottle PES analyzer. The third-generation ESI-PES apparatus developed recently at Brown University is shown schematically in Fig.…”

Characterizing the Intramolecular H-bond and Secondary Structure in Methylated GlyGlyH+ with H2 Predissociation Spectroscopy

“…Infrared spectra were recorded on the Yale tandem time-offlight photofragmentation mass spectrometer, which has recently been fitted with an electrospray ionization (ESI) source coupled to a cryogenic, quadrupole ion trap designed closely after that of Wang et al [46] and described in detail previously [47]. Millimolar solutions of GlyGly and its methylated derivatives were prepared by dissolving the solids in a mixture of methanol, water, and 0.1% formic acid in a volume ratio of 49.5:49.5:1.…”

Vibronic spectra of protonated hydroxypyridines: contributions of prefulvenic and planar structures

“…The setup is similar to the one developed by X. B. Wang et al 35 and has already been described elsewhere. 36,37 The protonated species are produced from an Electrospray Ion Source (ESI).…”