Atomic fluorescence emitted from a corona discharge in helium above and below saturated vapour pressure

Abstract

Abstract.A new apparatus was constructed to investigate the visible and near infrared fluorescence spectroscopy of electronically excited helium over a wide range of pressures and temperatures, covering both the gaseous and liquid phases. To achieve sufficient throughput, increased sensitivity was established by employing a micro-discharge cell and a high performance lens system that allows for a large collection solid angle. With this set-up, several thousand spectra were recorded. The atomic 3s1 S → 2p 1 P and 3s 3 S → 2p 3 P atomic transitions showed line shifts, spectral broadening and intensity changes that were dependent in magnitude on pressure, temperature and thermodynamic phase. While in the gas phase the lines showed little dependency on the discharge cell temperature, the opposite was observed for the liquid phase, suggesting that a significant number of atoms were solvated. Triplet lines were up to a factor of 50 times stronger in intensity than the singlet lines, depending on pressure. When taking the particle density into account, this effect was stronger in the gas phase than in the liquid phase of helium. This was attributed to the recombination of He2 + , He3 + and He4 + with electrons, which is facilitated in the gas phase because of the significantly higher mobility.

Relaxation dynamics of 3He and 4He clusters and droplets studied using near infrared and visible fluorescence excitation spectroscopy

“…41–49 It builds strongly on previous work on electronically excited bulk liquid and the use of fluorescence spectroscopy for detection. 50–64 The topic of electronically excited helium clusters has also been addressed by theory. 65–72…”

“…[41][42][43][44][45][46][47][48][49] It builds strongly on previous work on electronically excited bulk liquid and the use of fluorescence spectroscopy for detection. [50][51][52][53][54][55][56][57][58][59][60][61][62][63][64] The topic of electronically excited helium clusters has also been addressed by theory. [65][66][67][68][69][70][71][72] Previous studies of electronically excited 4 He clusters established the presence of perturbed atomic-like states related to the 2p 1 P ' 1s 1 S and dipole-forbidden 2s 1 S ' 1s 1 S transitions of helium atoms.…”

Dynamics of molecular systems

“…Baturo et al [11] reported an experimental study on the predissociation of the Rg-I 2 (Rg = rare gas atom) van der Waals complexes in their ion-pair excited electronic state. Finally, details on a new apparatus to investigate the visible and near infrared fluorescence spectroscopy of electronically excited helium over a wide range of pressures and temperatures in gaseous and liquid phases have been presented by Shiltagh et al [12].…”