Physical Review A

n -changing collisions in intermediate Rydberg states of Li induced by collisions with ground-state parent atoms

Bernard Dubreuil

Published May 1, 1983• 6 citations

Abstract

Two-step laser-induced-fluorescence techniques are used to investigate $n$-changing collisional processes $\mathrm{Li}(n=9)+\mathrm{Li}(2^{2}S)\ensuremath{\rightarrow}\mathrm{Li}({n}^{\ensuremath{'}}\ensuremath{\ne}n) +\mathrm{Li}(2^{2}S)+\ensuremath{\Delta}E_{\mathrm{nn}}^{\ensuremath{'}}$ in a temperature-controlled lithium heat-pipe oven. Numerical identification of the resonance- and collision-induced fluorescences with the hydrogenic rate equations describing the time variation of the $n=7,8,9,10,11$ populations allows the determination of collisional transfer and quenching rate coefficients. $n$-changing collisions with $\ensuremath{\Delta}n=|n\ensuremath{-}{n}^{\ensuremath{'}}|=1$ predominate, and the quenching rate coefficients are found nearly independent of $n: {k}_{n}\ensuremath{\sim}1.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$ ${\mathrm{cm}}^{3}$${\mathrm{s}}^{\ensuremath{-}1}$.

DOI: 10.1103/physreva.27.2479

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l-changing collisions in the intermediate Rydberg states of lithium

Mimoun Harnafi, Bernard Dubreuil

Physical Review AMar 1, 19859 citations

Quenching and excitation transfers in n=3 lithium sublevels

Catherine Chaleard, Bernard Dubreuil, A. Catherinot

Physical Review ASep 1, 198221 citations

l- andn-changing processes in the Rydberg states of Li induced by thermal collisions with H2 , N2 ,CO, and D2

Bernard Dubreuil, Mimoun Harnafi

Physical Review AAug 1, 19863 citations

4D2→4F2 excitation transfer in Li induced by collisions with Li, He, and Ar ground-state atoms

Bernard Dubreuil, Catherine Chaleard

Physical Review AFeb 1, 198410 citations

l- andn-changing collisions during interaction of a pulsed beam of Li Rydberg atoms with CO2

Bernard Dubreuil, Mimoun Harnafi

Physical Review AJul 1, 19891 citation

Laser-induced collisional-energy transfer in thermal collisions of lithium and strontium

Friedhelm Dorsch, S. Geltman, P. E. Toschek

Physical Review AApr 1, 198835 citations

Physical Review A

n -changing collisions in intermediate Rydberg states of Li induced by collisions with ground-state parent atoms

Bernard Dubreuil

Published May 1, 1983• 6 citations

Publisher

Abstract

Two-step laser-induced-fluorescence techniques are used to investigate

n

-changing collisional processes

\mathrm{Li}(n=9)+\mathrm{Li}(2^{2}S)\ensuremath{\rightarrow}\mathrm{Li}({n}^{\ensuremath{'}}\ensuremath{\ne}n) +\mathrm{Li}(2^{2}S)+\ensuremath{\Delta}E_{\mathrm{nn}}^{\ensuremath{'}}

in a temperature-controlled lithium heat-pipe oven. Numerical identification of the resonance- and collision-induced fluorescences with the hydrogenic rate equations describing the time variation of the

n=7,8,9,10,11

populations allows the determination of collisional transfer and quenching rate coefficients.

n

-changing collisions with

\ensuremath{\Delta}n=|n\ensuremath{-}{n}^{\ensuremath{'}}|=1

predominate, and the quenching rate coefficients are found nearly independent of

n: {k}_{n}\ensuremath{\sim}1.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}

{\mathrm{cm}}^{3}$${\mathrm{s}}^{\ensuremath{-}1}

DOI: 10.1103/physreva.27.2479

Related papers

l-changing collisions in the intermediate Rydberg states of lithium

Mimoun Harnafi, Bernard Dubreuil

l-mixing collisions Li( ${n}^{2}$ D)+X\ensuremath{\rightarrow}Li( ${n}^{2}$ L,L>2)+X induced in Rydberg states of lithium (n=4,5,...,13) by rare-gas atoms or Li ground-state atoms are studied in a heat-pipe arrangement. The l-mixing cross sections deduced from the time analysis of the ${n}^{2}$ D laser-induced fluorescence agree with experimental values obtained with the heavier alkali-metal atoms and with different theoretical models developed for quasielastic Rydberg-electron--target collisions. Quenching of the ${n}^{2}$ D fluorescence at higher rare-gas pressures is interpreted as inelastic collisional transfer of the L\ensuremath{\ge}1 mixed states to the nonhydrogenic S sublevel. Finally the radiative lifetimes of the ${n}^{2}$ D states and ${n}^{2}$ L mixed states with L\ensuremath{\ge}1 are deduced, respectively, from the low-pressure limit and intermediate-pressure study of the ${n}^{2}$ D fluorescence relaxation rate.l-mixing collisions Li(${n}^{2}$D)+X\ensuremath{\rightarrow}Li(${n}^{2}$L,L>2)+X induced in Rydberg states of lithium (n=4,5,...,13) by rare-gas atoms or Li ground-state atoms are studied in a heat-pipe arrangement. The l-mixing cross sections deduced from the time analysis of the ${n}^{2}$D laser-induced fluorescence agree with experimental values obtained with the heavier alkali-metal atoms and with different theoretical models developed for quasielastic Rydberg-electron--target collisions. Quenching of the ${n}^{2}$D fluorescence at higher rare-gas pressures is interpreted as inelastic collisional transfer of the L\ensuremath{\ge}1 mixed states to the nonhydrogenic S sublevel. Finally the radiative lifetimes of the ${n}^{2}$D states and ${n}^{2}$L mixed states with L\ensuremath{\ge}1 are deduced, respectively, from the low-pressure limit and intermediate-pressure study of the ${n}^{2}$D fluorescence relaxation rate.

Physical Review AMar 1, 19859 citations

Quenching and excitation transfers in n=3 lithium sublevels

Catherine Chaleard, Bernard Dubreuil, A. Catherinot

Quenching and excitation-transfer processes involving the $3^{2}P$ and $3^{2}D$ states of the Li atom are studied in a temperature-controlled heat-pipe oven with the use of two-step laser excitation of the $4^{2}S$ state followed by radiative cascade towards the $3^{2}P$ state. Numerical identification of the collision-induced $3^{2}D\ensuremath{\rightarrow}2^{2}P$ fluorescence with a three-level model allows the determination of radiative coefficients and collisional rate coefficients. $4^{2}S$ , $3^{2}D$ , and $3^{2}P$ radiative lifetimes are found to be in agreement with accepted values. Quenching and excitation transfer strongly depend on the colliding atoms. Rate coefficients for the $3^{2}D\ensuremath{\rightarrow}3^{2}P$ excitation processes induced by Li, He, and Ne ground-state atoms are measured in the ratio 1.05: 0.23: 0.02 expressed in ${10}^{\ensuremath{-}9}$ ${\mathrm{sec}}^{\ensuremath{-}1}$ ${\mathrm{cm}}^{3}$ .Quenching and excitation-transfer processes involving the $3^{2}P$ and $3^{2}D$ states of the Li atom are studied in a temperature-controlled heat-pipe oven with the use of two-step laser excitation of the $4^{2}S$ state followed by radiative cascade towards the $3^{2}P$ state. Numerical identification of the collision-induced $3^{2}D\ensuremath{\rightarrow}2^{2}P$ fluorescence with a three-level model allows the determination of radiative coefficients and collisional rate coefficients. $4^{2}S$, $3^{2}D$, and $3^{2}P$ radiative lifetimes are found to be in agreement with accepted values. Quenching and excitation transfer strongly depend on the colliding atoms. Rate coefficients for the $3^{2}D\ensuremath{\rightarrow}3^{2}P$ excitation processes induced by Li, He, and Ne ground-state atoms are measured in the ratio 1.05: 0.23: 0.02 expressed in ${10}^{\ensuremath{-}9}$ ${\mathrm{sec}}^{\ensuremath{-}1}$ ${\mathrm{cm}}^{3}$.

Physical Review ASep 1, 198221 citations

l- andn-changing processes in the Rydberg states of Li induced by thermal collisions with H2 , N2 ,CO, and D2

Bernard Dubreuil, Mimoun Harnafi

Collisional transfers induced in the n=6--13 Li Rydberg states by ${\mathrm{H}}_{2}$ , ${\mathrm{N}}_{2}$ , and CO molecules have been experimentally studied in a heat-pipe oven. The l-mixing cross sections have been deduced from the fast component of the population relaxations following pulsed laser excitation. The order of magnitude of these cross sections ( ${10}^{3}$ A ${\r{}}^{2}$ ) is well predicted by the existing theories. For large n, the cross sections stay approximately constant. This can be partly explained by the influence of inelastic processes such as n changing. In the particular case of ${\mathrm{H}}_{2}$ , n-changing collisions have been identified by the fluorescence starting from the n'=n\ifmmode\pm\else\textpm\fi{}1, n-2 levels. Cross sections of the order of 10 A ${\r{}}^{2}$ have been measured. The systematic study of the n-changing cross sections as a function of the transferred energy shows some evidence of resonance phenomena corresponding to an energy exchange between the Rydberg electron and the molecular rotation. This effect is also observed when ${\mathrm{H}}_{2}$ is replaced by ${\mathrm{D}}_{2}$ . These resonances are well described by the theory of Petitjean and Gounand based on the e-quadrupolar interaction.Collisional transfers induced in the n=6--13 Li Rydberg states by ${\mathrm{H}}_{2}$, ${\mathrm{N}}_{2}$, and CO molecules have been experimentally studied in a heat-pipe oven. The l-mixing cross sections have been deduced from the fast component of the population relaxations following pulsed laser excitation. The order of magnitude of these cross sections (${10}^{3}$ A${\r{}}^{2}$) is well predicted by the existing theories. For large n, the cross sections stay approximately constant. This can be partly explained by the influence of inelastic processes such as n changing. In the particular case of ${\mathrm{H}}_{2}$, n-changing collisions have been identified by the fluorescence starting from the n'=n\ifmmode\pm\else\textpm\fi{}1, n-2 levels. Cross sections of the order of 10 A${\r{}}^{2}$ have been measured. The systematic study of the n-changing cross sections as a function of the transferred energy shows some evidence of resonance phenomena corresponding to an energy exchange between the Rydberg electron and the molecular rotation. This effect is also observed when ${\mathrm{H}}_{2}$ is replaced by ${\mathrm{D}}_{2}$. These resonances are well described by the theory of Petitjean and Gounand based on the e-quadrupolar interaction.

Physical Review AAug 1, 19863 citations

4D2→4F2 excitation transfer in Li induced by collisions with Li, He, and Ar ground-state atoms

Bernard Dubreuil, Catherine Chaleard

Excitation transfers between the $4^{2}D$ and $4^{2}F$ states of lithium are studied in a temperature-controlled heat-pipe oven. These transfers are induced by collisions with Li, He, and Ar ground-state atoms. Quenching cross section and radiative rates are also measured. For the excitation transfer process, the thermally averaged cross sections are, respectively, ${\ensuremath{\sigma}}^{\mathrm{Li}}=400$ ${\mathrm{\AA{}}}^{2}$ , ${\ensuremath{\sigma}}^{\mathrm{He}}=120$ ${\mathrm{\AA{}}}^{2}$ , and ${\ensuremath{\sigma}}^{\mathrm{Ar}}=190$ ${\mathrm{\AA{}}}^{2}$ . These values agree with the experimental results of Gallagher in Na and the calculations of Gersten. Finally, the behavior of the $4^{2}D\ensuremath{-}4^{2}F$ two-level system in the $l$ -mixing regime is investigated in the case of Ar collisions.Excitation transfers between the $4^{2}D$ and $4^{2}F$ states of lithium are studied in a temperature-controlled heat-pipe oven. These transfers are induced by collisions with Li, He, and Ar ground-state atoms. Quenching cross section and radiative rates are also measured. For the excitation transfer process, the thermally averaged cross sections are, respectively, ${\ensuremath{\sigma}}^{\mathrm{Li}}=400$ ${\mathrm{\AA{}}}^{2}$, ${\ensuremath{\sigma}}^{\mathrm{He}}=120$ ${\mathrm{\AA{}}}^{2}$, and ${\ensuremath{\sigma}}^{\mathrm{Ar}}=190$ ${\mathrm{\AA{}}}^{2}$. These values agree with the experimental results of Gallagher in Na and the calculations of Gersten. Finally, the behavior of the $4^{2}D\ensuremath{-}4^{2}F$ two-level system in the $l$-mixing regime is investigated in the case of Ar collisions.

Physical Review AFeb 1, 198410 citations

l- andn-changing collisions during interaction of a pulsed beam of Li Rydberg atoms with CO2

Bernard Dubreuil, Mimoun Harnafi

The pulsed Li atomic beam produced in our experiment is based on controlled transversely-excited-atmospheric ${\mathrm{CO}}_{2}$ laser--induced ablation of a Li metal target. The atomic beam is propagated in vacuum or in ${\mathrm{CO}}_{2}$ gas at low pressure. Atoms in the beam are probed by laser-induced fluorescence spectroscopy. This allows the determination of time-of-flight and velocity distributions. Li Rydberg states (n=5--13) are populated in the beam by two-step pulsed-laser excitation. The excited atoms interact with ${\mathrm{CO}}_{2}$ molecules. l- and n-changing cross sections are deduced from the time evolution of the resonant or collision-induced fluorescence following this selective excitation. l-changing cross sections of the order of ${10}^{4}$ A ${\r{}}^{2}$ are measured; they increase with n as opposed to the plateau observed for ${\mathrm{Li}}^{\mathrm{*}}$ colliding with a diatomic molecule. This behavior is qualitatively well explained in the framework of the free-electron model. n\ensuremath{\rightarrow}n' changing processes with large cross sections (10--100 A ${\r{}}^{2}$ ) are also observed even in the case of large electronic energy change (\ensuremath{\Delta} ${E}_{\mathrm{nn}\mathcal{'}}$ ${>10}^{3}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$). These results can be interpreted in terms of resonant-electronic to vibrational energy transfers between Li Rydberg states and ${\mathrm{CO}}_{2}$ vibrational modes.The pulsed Li atomic beam produced in our experiment is based on controlled transversely-excited-atmospheric ${\mathrm{CO}}_{2}$ laser--induced ablation of a Li metal target. The atomic beam is propagated in vacuum or in ${\mathrm{CO}}_{2}$ gas at low pressure. Atoms in the beam are probed by laser-induced fluorescence spectroscopy. This allows the determination of time-of-flight and velocity distributions. Li Rydberg states (n=5--13) are populated in the beam by two-step pulsed-laser excitation. The excited atoms interact with ${\mathrm{CO}}_{2}$ molecules. l- and n-changing cross sections are deduced from the time evolution of the resonant or collision-induced fluorescence following this selective excitation. l-changing cross sections of the order of ${10}^{4}$ A${\r{}}^{2}$ are measured; they increase with n as opposed to the plateau observed for ${\mathrm{Li}}^{\mathrm{*}}$ colliding with a diatomic molecule. This behavior is qualitatively well explained in the framework of the free-electron model. n\ensuremath{\rightarrow}n' changing processes with large cross sections (10--100 A${\r{}}^{2}$) are also observed even in the case of large electronic energy change (\ensuremath{\Delta}${E}_{\mathrm{nn}\mathcal{'}}$${>10}^{3}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$). These results can be interpreted in terms of resonant-electronic to vibrational energy transfers between Li Rydberg states and ${\mathrm{CO}}_{2}$ vibrational modes.

Physical Review AJul 1, 19891 citation

Laser-induced collisional-energy transfer in thermal collisions of lithium and strontium

Friedhelm Dorsch, S. Geltman, P. E. Toschek

Fluorescence of Li excited by laser light and simultaneous thermal ${\mathrm{Sr}}^{\mathrm{*}}$ collisions in the reaction Sr(5p)+Li(2s)+\ensuremath{\Elzxh}\ensuremath{\omega} (\ensuremath{\lambda}=669.8 nm)\ensuremath{\rightarrow}Sr(5 ${s}^{2}$ )+Li(4d) shows an asymmetric excitation spectrum of the energy transfer versus \ensuremath{\lambda}. The peak variation with light intensity demonstrates the strong-field regime and verifies current models. A change in the slope of the quasistatic wing agrees with the result of a recent three-level model.Fluorescence of Li excited by laser light and simultaneous thermal ${\mathrm{Sr}}^{\mathrm{*}}$ collisions in the reaction Sr(5p)+Li(2s)+\ensuremath{\Elzxh}\ensuremath{\omega} (\ensuremath{\lambda}=669.8 nm)\ensuremath{\rightarrow}Sr(5${s}^{2}$)+Li(4d) shows an asymmetric excitation spectrum of the energy transfer versus \ensuremath{\lambda}. The peak variation with light intensity demonstrates the strong-field regime and verifies current models. A change in the slope of the quasistatic wing agrees with the result of a recent three-level model.

Physical Review AApr 1, 198835 citations

Two-step laser-induced-fluorescence techniques are used to investigate

n

-changing collisional processes

\mathrm{Li}(n=9)+\mathrm{Li}(2^{2}S)\ensuremath{\rightarrow}\mathrm{Li}({n}^{\ensuremath{'}}\ensuremath{\ne}n) +\mathrm{Li}(2^{2}S)+\ensuremath{\Delta}E_{\mathrm{nn}}^{\ensuremath{'}}

n=7,8,9,10,11

populations allows the determination of collisional transfer and quenching rate coefficients.

n

-changing collisions with

\ensuremath{\Delta}n=|n\ensuremath{-}{n}^{\ensuremath{'}}|=1

predominate, and the quenching rate coefficients are found nearly independent of

n: {k}_{n}\ensuremath{\sim}1.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}

{\mathrm{cm}}^{3}$${\mathrm{s}}^{\ensuremath{-}1}

l-mixing collisions Li(

{n}^{2}

D)+X\ensuremath{\rightarrow}Li(

{n}^{2}

L,L>2)+X induced in Rydberg states of lithium (n=4,5,...,13) by rare-gas atoms or Li ground-state atoms are studied in a heat-pipe arrangement. The l-mixing cross sections deduced from the time analysis of the

{n}^{2}

D laser-induced fluorescence agree with experimental values obtained with the heavier alkali-metal atoms and with different theoretical models developed for quasielastic Rydberg-electron--target collisions. Quenching of the

{n}^{2}

D fluorescence at higher rare-gas pressures is interpreted as inelastic collisional transfer of the L\ensuremath{\ge}1 mixed states to the nonhydrogenic S sublevel. Finally the radiative lifetimes of the

{n}^{2}

D states and

{n}^{2}

L mixed states with L\ensuremath{\ge}1 are deduced, respectively, from the low-pressure limit and intermediate-pressure study of the

{n}^{2}

D fluorescence relaxation rate.

Quenching and excitation-transfer processes involving the

3^{2}P

and

3^{2}D

states of the Li atom are studied in a temperature-controlled heat-pipe oven with the use of two-step laser excitation of the

4^{2}S

state followed by radiative cascade towards the

3^{2}P

state. Numerical identification of the collision-induced $3^{2}D\ensuremath{\rightarrow}2^{2}P$ fluorescence with a three-level model allows the determination of radiative coefficients and collisional rate coefficients.

4^{2}S

3^{2}D

, and

3^{2}P

radiative lifetimes are found to be in agreement with accepted values. Quenching and excitation transfer strongly depend on the colliding atoms. Rate coefficients for the $3^{2}D\ensuremath{\rightarrow}3^{2}P$ excitation processes induced by Li, He, and Ne ground-state atoms are measured in the ratio 1.05: 0.23: 0.02 expressed in ${10}^{\ensuremath{-}9}$ ${\mathrm{sec}}^{\ensuremath{-}1}$

{\mathrm{cm}}^{3}

Collisional transfers induced in the n=6--13 Li Rydberg states by

{\mathrm{H}}_{2}

{\mathrm{N}}_{2}

, and CO molecules have been experimentally studied in a heat-pipe oven. The l-mixing cross sections have been deduced from the fast component of the population relaxations following pulsed laser excitation. The order of magnitude of these cross sections (

{10}^{3}

{\r{}}^{2}

) is well predicted by the existing theories. For large n, the cross sections stay approximately constant. This can be partly explained by the influence of inelastic processes such as n changing. In the particular case of

{\mathrm{H}}_{2}

, n-changing collisions have been identified by the fluorescence starting from the n'=n\ifmmode\pm\else\textpm\fi{}1, n-2 levels. Cross sections of the order of 10 A

{\r{}}^{2}

have been measured. The systematic study of the n-changing cross sections as a function of the transferred energy shows some evidence of resonance phenomena corresponding to an energy exchange between the Rydberg electron and the molecular rotation. This effect is also observed when

{\mathrm{H}}_{2}

is replaced by

{\mathrm{D}}_{2}

. These resonances are well described by the theory of Petitjean and Gounand based on the e-quadrupolar interaction.

Excitation transfers between the

4^{2}D

and

4^{2}F

states of lithium are studied in a temperature-controlled heat-pipe oven. These transfers are induced by collisions with Li, He, and Ar ground-state atoms. Quenching cross section and radiative rates are also measured. For the excitation transfer process, the thermally averaged cross sections are, respectively, ${\ensuremath{\sigma}}^{\mathrm{Li}}=400$

{\mathrm{\AA{}}}^{2}

, ${\ensuremath{\sigma}}^{\mathrm{He}}=120$

{\mathrm{\AA{}}}^{2}

, and ${\ensuremath{\sigma}}^{\mathrm{Ar}}=190$

{\mathrm{\AA{}}}^{2}

. These values agree with the experimental results of Gallagher in Na and the calculations of Gersten. Finally, the behavior of the $4^{2}D\ensuremath{-}4^{2}F$ two-level system in the

l

-mixing regime is investigated in the case of Ar collisions.

The pulsed Li atomic beam produced in our experiment is based on controlled transversely-excited-atmospheric

{\mathrm{CO}}_{2}

laser--induced ablation of a Li metal target. The atomic beam is propagated in vacuum or in

{\mathrm{CO}}_{2}

gas at low pressure. Atoms in the beam are probed by laser-induced fluorescence spectroscopy. This allows the determination of time-of-flight and velocity distributions. Li Rydberg states (n=5--13) are populated in the beam by two-step pulsed-laser excitation. The excited atoms interact with

{\mathrm{CO}}_{2}

molecules. l- and n-changing cross sections are deduced from the time evolution of the resonant or collision-induced fluorescence following this selective excitation. l-changing cross sections of the order of

{10}^{4}

{\r{}}^{2}

are measured; they increase with n as opposed to the plateau observed for

{\mathrm{Li}}^{\mathrm{*}}

colliding with a diatomic molecule. This behavior is qualitatively well explained in the framework of the free-electron model. n\ensuremath{\rightarrow}n' changing processes with large cross sections (10--100 A

{\r{}}^{2}

) are also observed even in the case of large electronic energy change (\ensuremath{\Delta}

{E}_{\mathrm{nn}\mathcal{'}}

{>10}^{3}

${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$). These results can be interpreted in terms of resonant-electronic to vibrational energy transfers between Li Rydberg states and

{\mathrm{CO}}_{2}

vibrational modes.

Fluorescence of Li excited by laser light and simultaneous thermal

{\mathrm{Sr}}^{\mathrm{*}}

collisions in the reaction Sr(5p)+Li(2s)+\ensuremath{\Elzxh}\ensuremath{\omega} (\ensuremath{\lambda}=669.8 nm)\ensuremath{\rightarrow}Sr(5

{s}^{2}

)+Li(4d) shows an asymmetric excitation spectrum of the energy transfer versus \ensuremath{\lambda}. The peak variation with light intensity demonstrates the strong-field regime and verifies current models. A change in the slope of the quasistatic wing agrees with the result of a recent three-level model.