Lifetime of the He2(e), He2(d) and He2(f) states

Abstract

10z' (19_+ 5) ns. From the time integrated fluorescence data the collisional quenching rates between the above states were determined.

Photodynamics in superfluid helium: Femtosecond laser-induced ionization, charge recombination, and preparation of molecular Rydberg states

“…The d→b fluorescence decays with a time constant of 25 ns, which corresponds to the radiative lifetime of the d state in the gas phase. 56 The f and e states decay within the detector response time of 10 ns, faster than their gas-phase radiative lifetimes of 20 and 60 ns, respectively. 56 acting as a bottleneck in the electronic cascade.…”

“…56 The f and e states decay within the detector response time of 10 ns, faster than their gas-phase radiative lifetimes of 20 and 60 ns, respectively. 56 acting as a bottleneck in the electronic cascade. Indeed, fast collisionally induced excitation transfer, with gas kinetic rate constants of the order of 10 Ϫ10 cm 3 /s, is observed among these three states in the gas phase.…”

“…Indeed, fast collisionally induced excitation transfer, with gas kinetic rate constants of the order of 10 Ϫ10 cm 3 /s, is observed among these three states in the gas phase. 56 The important implication of the fast interconversion is that the three observed fluorescence bands may originate from a single excitation transition.…”

Trace Detection of Metastable Helium Molecules in Superfluid Helium by Laser-Induced Fluorescence

“…Molecules in the d 3 Σ + u then decay to the b 3 Π g with a 90% branching ratio, emitting an easily detected photon at 640 nm. The lifetime of the d 3 Σ + u → b 3 Π g transition has been measured to be 25 ns in both liquid [20] and gaseous [21] helium, demonstrating that there is little non-radiative quenching of the d 3 Σ + u state. Finally, the b 3 Π g state is non-radiatively quenched before it can decay [7], returning to the a 3 Σ + u state where it is again sensitive to the probe laser.…”

Oxygen atoms and nitrogen molecules as spectroscopic probes for the temperature determination in non-equilibrium cryogenic helium plasma jets

“…These facts reveal the presence of concurrent mechanisms for the population of the excited states and for the collisional transfers within rotational levels [6]. The observed high T rot of the excited states probably results from the very short life times ~ 10 ns [7], reaching ~ 1 ns, for the high Rydberg states of He 2 [8]. It was shown that the rotational spectra of He 2 * molecules may be used for gas temperature measurements in the glow discharges at rather high pressure and current values [9,10] while a typical emission spectrum of the d 3 Σ + u -b 3 Π g transition of He 2 * from a cryogenic helium plasma jet at T< 100 K is shown in Fig.…”