Experimental methods for studies of ion – molecule reaktions and of ion – electron rekombination

Time dependence of the value of recombination rate coefficient for H3+ ions with electrons
Not a simple problem

Different experiments
Ion Storage Ring
Afterglow plasma
+ No buffer gas
+ Excellent energy resolution
Complicated estimation of cross section from measured data
Rotational temperature of ions in the ring can be >= 300 K
+ Many collisions of ions with buffer gas particles – effective thermalization
+ The measured quantity is thermal rate coefficient
Complicated chemical kinetics
Presence of third bodies can influence the recombination

Ion storage ring
Figure 1: Design model of the CSR showing the electrostatic ion optical elements (enlarged in circuits), the injection line, the electron cooler (straight section at the right side) and the reaction microscope (straight section at the left side)
(A) Scheme of the CSR ring structure with the injected and stored HeH+ ion beam (red), merged electron beam (blue), reaction products (green), and particle detector. (B) Reaction scheme and position-sensitive detection of coincident fragments. (C) Equilibrium rotational state populations of HeH+ for previous studies (300 K) and the estimated radiation field in the CSR.

Recombination of ions in specific quantum state

Rekombination of H3+ ions with electrons
Neutral assisted ternary recombination:
Electron assisted ternary recombination:
Formation of H5+ and its subsequent recombination with electrons:
Glosík J., Dohnal P. et al., Plasma Sources Sci. Technol. 24(6), 065017, 2015

Stationary afterglow plasma
Combination of Stationary afterglow and absorption spectroscopy

Stationary afterglow plasma
AISA – Advanced Integrated Stationary Afterglow
Mass spectrometer + Langmuir probe diagnostics
Phys. Rev. Lett., 88 (4): Art. No. 044802 (4 pages), 2002.

Stationary afterglow plasma
Microwave diagnostics + mass spectrometry

Microwave diagnostics of plasma
Plasma conductivity
Change of resonant frequency and resonator quality:
Plasma frequency

Microwave diagnostics of plasma
Sicha et al., Czech. J. Phys. B 20, 684, 1970
From the shift of resonant frequency we can get electron number density

Electron number density measurement
Microwave diagnostics of plasma

SA-CRDS apparatus
CRDS – Cavity Ring Down Spectroscopy
SA – Stationary Afterglow
Highly reflective mirror
Discharge tube diameter– 1.5 cm
He buffer gas flow ~ 400 – 1600 sccm
Pressure ~ 200 – 1500 Pa
Temperature range ~ 77 – 300 K

Cavity ringdown spectroscopy
First used for mirror reflectivity determination (Herbelin et al. 1980).
Later, the dependence of ring-down time on absorption between the mirrors was observed (O‘Keefe et al. 1988)
Herbelin et al., Appl. Opt. 19, 144, 1980.
O‘Keefe et al., Rev. Sci. Instrum. 59, 2544, 1988.
Highly reflective mirrors by Layertec (diameter 6.3 mm, reflectivity R = 99.99 %)

SA-CRDS
The time evolution of ion number density is measured (of particular quantum states)
Kinetic temperature can be determined from Doppler broadening of absorption lines
Rotational temperature is given by relative populations of rotational states

Cryo-SA-CRDS

Cryo-SA-CRDS

Cryo-SA-CRDS
Plašil, R; Dohnal, P; Kálosi, Á; Roučka, Š; Shapko, D; Rednyk, S; Johnsen, R; Glosík, J, Rev. Sci. Instrum., 89: 063116, 2018.

H3+ (again)
The lowest rotational states of the vibrational ground state
Para
I = 1/2
I = 3/2

Cryo-SA-CRDS
At 30 K, we can change the population of the of the lowest state of H3+ from 40% to 80% of all ions. The rest of the ions are mainly in the (1,0) state.

Rekombination of H3+ ions in specific quantum state

Combination of CRDS and microwave diagnostics

Studied ion is not dominant in plasma

Flowing afterglow plasma

Flowing afterglow plasma

FALP, SIFT, SIFDT
FALP – Flowing Afterglow with Langmuir Probe
SIFT – Selective Ion Flow Tube
SIFDT – Selective Ion Flow Drift Tube

FALP, SIFT, SIFDT
FALP – study of electron – ion recombination
SIFT – study of ion – molecule reactions
Measurement of ion mobility

Cryo-FALP II
Cryogenic Flowing Afterglow with Langmuir Probe
Flowtube diameter – 5 cm
He buffer gas flow ~ 2500– 6000 sccm
Pressure ~ 200 – 2000 Pa
Temperature range ~ 40 – 300 K

Cryo-FALP II
The evolution of electron number density along the flowtube (i.e. in time) is measured
It is possible to determine the electron energy distribution function and their temperature

Recombination of Ar+ ions with elekcrons, dependence on ne
Kotrík T., Dohnal P., Roučka Š., Jusko P., Plašil R., Glosík J., Johnsen R., Phys. Rev. A 83, 032720, 2011.
Kotrík T., Dohnal P., Rubovič P., Plašil R., Roučka Š., Opanasiuk S., Glosík J., Eur. Phys. J.-Appl. Phys. 56, 24011, 2011.

Recombination of Ar+ ions with elekcrons, dependence on helium pressure
Dohnal P., Rubovič P., Kotrík T., Hejduk M., Plašil R., Johnsen R., Glosík J., Phys. Rev. A 87, 052716, 2013.

Calibration of Langmuir Probe
Rekombination of O2+ ions with electrons is a well known process (many studies in last 50 years)
Three body (helium assisted) recombination is at given conditions negligible
The goal is to determine the electron number density with the best possible precision

22 rf pole ion trap
Many configurations for different experiments
Cold Heads at 22PT and H atom source work down to 11 K a 7 K
Ions produced in Storage Ion Source (SIS)
Only ions selected by QP mass filter enter the trap
After set storage time, the ions from the trap are mass selected and detected by MCP

22 rf pole ion trap

O- + D2
Plašil, R; Tran, TD; Roučka, Š; Jusko, P; Mulin, D; Zymak, I; Rednyk, S; Kovalenko, A; Dohnal, P; Glosík, J; Houfek, K; Táborský, J; Cížek, M, Phys. Rev. A, 96 (6): 062703 ,2017.