九州大学大学院総合理工学報告第 46 巻 第 1 号 7-18 頁 令和 6 年 9 月

Engineering Sciences Reports, Kyushu University
Vol. 46, No. 1, pp. 7-18, SEP, 2024

Rovibrational Distribution of CS(A1Π) Produced by
Collisions of Metastable Kr(3P2) Atoms with CS2
in the Flowing Afterglow
Masaharu TSUJI,*1,2† Masafumi NAKAMURA,*3
Nobuo KANEKO*3 and Hiroshi OBASE*4
E-mail of corresponding author: tsuji@cm.kyushu-u.ac.jp†(Received March 5, 2024, accepted March 13, 2024)
Rovibrational distribution of CS(A1Π) produced by the Kr(3P2)/CS2 reaction was studied byobserving CS(A1Π−X1Σ+) emission in the flowing afterglow. The CS(A−X) emission from 𝑣𝑣 ′ = 0–5 was
identified in the 245−275 nm region. The band intensities from the CS(A:𝑣𝑣 ′ = 1–4) levels were combinedwith calculated RKR Franck-Condon factors (FCFs) to analyze the dependence of the electronictransition moment on r-centroid. The relative vibrational formation rates of CS(A:𝑣𝑣 ′ = 0–5), 𝑃𝑃𝑣𝑣′ , were
estimated to be 1.00:0.94:0.65:0.41:0.19:0.08. The rotational distributions of CS(A: 𝑣𝑣 ′ = 0–5) wereexpressed by single Boltzmann rotational temperatures (𝑇𝑇𝑅𝑅 ) of 2300, 2000, 1800, 1500, 1400, and 1200
K, respectively. From the observed 𝑃𝑃𝑣𝑣′ and 𝑇𝑇𝑅𝑅 data, the average fractions of excess energy deposited
into vibrational and rotational energies of CS(A), and relative translational energy of products were
determined to be < f v > =25%, < f r > =24%, and < f t > =51%, respectively. The observed 𝑃𝑃𝑣𝑣′ and 𝑇𝑇𝑅𝑅 data ofCS(A:𝑣𝑣 ′ = 0–5) were compared with previous data for the Ar(3P2)/CS2 reaction and vacuum ultraviolet(VUV) photoexcitation. They were also compared with statistical prior vibrational and rotational
distributions to examine the reaction dynamics. Possible precursor Rydberg states of CS2** in the
Kr(3P2)/CS2 and Ar(3P2)/CS2 reactions were discussed from reported fluorescence cross section data.
Key words: Flowing afterglow, Metastable Kr(3P2) atom, CS2, Energy transfer, Dissociative excitation,
CS(A-X) emission, Electronic transition moment, Rovibrational distribution, Rotationaltemperature, Prior distribution, Rydberg state

1.

Introduction

Optical spectroscopic studies on energy
transfer reactions between rare gas metastableatoms and CS2 have been extensively studied
for He(23S:19.82 eV), Ne(3P2:16.62 eV and
3P0:16.72 eV), Ar(3P2:11.55 eV and 3P0:11.72 eV),and Xe(3P2:8.32 eV and 3P0:9.45 eV) atoms.1-10)
In the reactions of He* and Ne* atoms withhigher excitation energy than the ionization
� 2Πu:12.7
� 2Πg:10.07 eV, A
potentials of CS2+( X+2� Σu :14.48 eV), major emitting producteV, B
channels are Penning ionization leading to�2Πu, B�2Σ+) states:1-5)
excited CS2+(A*1Institute for Materials Chemistry and Engineering,and Research and Education Center of GreenTechnology*2 Department of Molecular Science and Technology*3 Department of Molecular Science and Technology,
Graduate Student*4 Research Institute of Industrial Science, Kyushu
University

He(23S) + CS2
�2Πu, B�2Σu+) + He + e-, (1)→ CS2+(A3
Ne( P2,0) + CS2
�2Πu, B�2Σu+) + Ne + e-. (2)→ CS2+(AIn the He and Ne afterglow reaction of CS2,
besides the above Penning ionization processes,
the following electron-ion recombination
process leading to excited CS(A1Π,a3Π) states
have been observed:1-3,8)
CS2+ + e- → CS(A1Π, a3Π) + S(3)Here, CS2+ ions and electrons are dominantly
formed by He(23S)/CS2 and Ne(3P2,0)/CS2
Penning ionization such as processes (1) and (2).
Molek et al.11) determined vibrational
distributions of CS(A1Π:𝑣𝑣 ′ = 0−4, a3Π:𝑣𝑣 ′ = 0−2)
in process (3) by using a flowing afterglow (FA)method.
In the Ar* and Xe* reactions with lower
excitation energy than the ionization potential
�), major emitting product channelsof CS2+ (A8Rovibrational Distribution of CS(A) Produced by Collisions of Kr(3P2) with CS2 in the Flowing Afterglow

are the formation of CS(A1Π) and/or CS(a3Π) by
dissociative excitation, respectively:6-10)
Ar(3P2,0) + CS2 → CS(A1Π, a3Π) + S + Ar, (4)(5)
Xe(3P2,0) + CS2 → CS(a3Π) + S + Xe.
The vibrational distribution of CS(A) in process(4) has been determined by Marcoux et al.,8)Wu,9) and Xu et al.10) Marcoux et al.8)
determined the vibrational population ofCS(A: 𝑣𝑣 ′ = 0−5) in the Ar FA. They alsomeasured the dependence of vibrational
distribution of CS(A:𝑣𝑣 ′ = 0−5) in process (3) on
the He buffer gas pressure in the He FA toexamine vibrational relaxation by collisions
with the He gas. Wu9) observed CS(A−X)
emission in the Ar FA. He noticed that besides
the Ar(3P2)/CS2 reaction, CS2+/e- recombination
reaction (3) may participate in the formation ofCS(A), because major output channel (74±17%)of the Ar(3P2)/CS2 reaction is Penningionization:12)
�) + Ar + e-,
Ar(3P2) + CS2 → CS2+(X(6).

(𝑃𝑃𝑣𝑣′ /𝑃𝑃𝑣𝑣′=0 ) = (𝑁𝑁𝑣𝑣′ ⁄𝑁𝑁𝑣𝑣′=0 ) (𝜏𝜏𝑣𝑣′=0 ⁄𝜏𝜏𝑣𝑣′ ),(7)

where precursor CS2+ and e- are formed
simultaneously. No effects of SF6 addition as a
typical electron scavenger led him to conclude
that electron-ion recombination process (3) was
insignificant in their condition. It was therefore
concluded that CS(A−X) emission results
exclusively from the Ar(3P2)/CS2 reaction (4).
Wu determined the relative vibrational
formation rate of CS(A: 𝑣𝑣 ′ = 0−5), 𝑃𝑃𝑣𝑣′ , in theAr(3P2)/CS2 reaction using the relation,is steady-state vibrational
where
𝑁𝑁𝑣𝑣′
population and 𝜏𝜏𝑣𝑣′ is the radiative lifetime of𝑣𝑣′ level measured by Carlson et al.13) Since the𝜏𝜏𝑣𝑣′ value increases from 185 ns to 225, 220, 230,
235, and 255 ns with increasing the vibrational
level from 𝑣𝑣 ′ = 0 to 𝑣𝑣 ′ = 1−5, respectively,13) 𝑃𝑃𝑣𝑣′
values for 𝑣𝑣 ′ = 1−5 are smaller thanvalues by 18−27%.
corresponding
𝑁𝑁𝑣𝑣′
Although Wu did not compare his 𝑁𝑁𝑣𝑣′
distribution with previous pioneering data of
Marcoux et al.8) measured in the same Ar FA,
it was much lower than that of Marcoux et al.8)
Xu et al.10) measured rovibrational distributionof CS(A) in the Ar(3P2)/CS2 reaction using FA
coupled with a low-pressure chamber. The
observed 𝑃𝑃𝑣𝑣′ distribution was more excitedthan that of Wu.7) They attributed highvibrational excitation in their low-pressure
experiment to the great reduction of vibrational

relaxation of CS(A: 𝑣𝑣 ′ = 1−5) by collision withbuffer Ar gas. The rotational distribution
decreased with an increase in 𝑣𝑣 ′ from 10 000±
300 K for 𝑣𝑣 ′ = 0 to 5600±300 K for 𝑣𝑣 ′ = 5. Xu etal.10) did not compare their vibrational
distribution with the 𝑁𝑁𝑣𝑣′ distribution of
Marcoux et al.8) When the 𝑃𝑃𝑣𝑣′ distribution of
Marcoux et al. was calculated using Eq. (7),difference in the 𝑃𝑃𝑣𝑣′ distribution between thetwo experiments was small.
Dissociative excitation pathways of CS2 by
the Ar(3P2)/CS2 reaction leading to CS(A) has
been discussed by Wu9) and Xu et al.10) Wu
reportedthat
CS(A)originatesfrompredissociation of the Rydberg state converging
into the ground state of CS2+ below theionization limit, via a very steep repulsive
potential curve. He concluded that a significant
amount of excess energy is deposited intotranslational energy because of low vibrational
excitation of CS(A). Although Xu et al.10)
reported that CS(A) is formed via at least five
steps E-E transfer involving Rydberg state,possible Rydberg states were not discussed.
Coxon et al.1) observed CS(A−X) emission in
the He afterglow reaction of CS2 anddetermined the dependence of electronictransition moment on the r-centroid from the𝑣𝑣 ′ =
0−4
intensity
distributionsof𝑣𝑣" -progressions. However, there was a large
variation in their data with respect to thefitting line.
Although optical spectroscopic studies onenergy-transfer reactions of He*, Ne*, Ar*, andXe* atoms with CS2 have been carried out, thatof Kr* has not been reported to our best
knowledge. The total reaction rate constant of
the Kr(3P2)/CS2 reaction has been measured as
8.0 × 10-10 cm3s-1 at 300 K by using an FA
technique.14) This value is smaller than that for
the Ar(3P2)/CS2 reaction by 25% (1.06 ×10-9
cm3s-1).14)
VUV photolysis of CS2 has been studied by
Lee and Judge15) and Ashhold et. al.16) Lee andJudge observed CS(A−X) emission by VUVphotons in the 123.9−68.6 nm (10.01−18.07 eV)region and determined 𝑁𝑁𝑣𝑣′ distributions at
92.3 nm (13.43 eV) and 123.9 nm (10.01 eV).
Ashfold et al. measured CS(A−X) emission by
VUV photons in the 130.4−121.6 nm(9.51−10.20 eV) range under better opticalresolution than that of Lee and Judge. They
determined the dependence of 𝑁𝑁𝑣𝑣′ distribution
on the excitation wavelength. The rotationaltemperature of CS(A: 𝑣𝑣 ′ =0) under 130.4 nm(9.51 eV) excitation was determined from aspectral simulation.

令和 6 年度

九州大学大学院総合理工学報告

In the present study, the energy-transfer
reaction of metastable Kr(3P2:9.92 eV) atoms
with CS2 is investigated by observing CS(A−X)
emission in the FA. The dependence ofelectronic transition moment on r-centroid isdetermined from the intensity distribution of
𝑣𝑣 ′ =0−4 𝑣𝑣"-progressions of CS(A−X) emission,
𝑣𝑣 ′
where
overlappingwithhigher𝑣𝑣" -progressions can be reduced greatly. The
vibrational and rotational populations ofCS(A: 𝑣𝑣 ′ = 0−5) are determined. The 𝑃𝑃𝑣𝑣′
distribution is estimated from Eq. (7). The 𝑁𝑁𝑣𝑣′
and 𝑃𝑃𝑣𝑣′ data obtained in this study arecompared with the reported 𝑁𝑁𝑣𝑣′ and 𝑃𝑃𝑣𝑣′ datain the Ar(3P2)/CS2 reaction8-10) and 𝑁𝑁𝑣𝑣′ data in
VUV photoexcitation with similar energies(123.6 nm = 10.03 eV).16) The observed
rovibrational distributions are also comparedwith statistical prior ones to obtain informationon the reaction dynamics. Possible precursor
CS2** Rydberg states leading to CS(A) in the
Kr(3P2)/CS2 and Ar(3P2)/CS2 reactions are
discussed based on reported fluorescence
excitation spectra and cross section data in the
VUV region.17,18)

2.

Experimental

The FA apparatus was identical with thatused for the Kr(3P2)/CO reactions.19) In brief,argon gas (>purity 99.999%) was excited to the

第 46 巻第1号

9

metastable 3P2,0 states by a microwave
discharge operated at an Ar buffer gas pressureof about 0.1 Torr (1 Torr= 133.3 Pa). The
metastable Kr(3P2) atoms were generated byadding a small amount of Kr(> 99.995%:5−20
mTorr) gas to the Ar flow prior to the discharge.
CS2 was added from an orifice placed 10 cm
downstream from the center of microwave
discharge. The partial pressure of CS2 in thereaction zone was a few mTorr.
The emission spectra were observed with a 1
m monochromator (Jarrell Ash M2) equippedwith a 1200 grooves/mm grating, blazed at 300
nm. The spectral response curve of themonochromator with a Hamamatsu Photonics
R376 photomultiplier was calibrated by using astandard halogen lamp.

3.

Results and discussion

3.1 CS(A-X) emission from the Kr(3P2)/CS2
reaction and the dependence of electronictransition moment on r-centroid
Figure 1a shows a typical emission spectrum
obtained from the Kr(3P2)/CS2 reaction, where
the CS(A1Π−X1Σ+) emission system from𝑣𝑣 ′ = 0−5 vibrational levels is identified.
Emissions from Δ 𝑣𝑣 ′ = 1, 0, and -1 sequences
are much stronger than those of Δ 𝑣𝑣 ′ = 2
sequence due to low vibrational excitation
above 𝑣𝑣 ′ = 3. For comparison, CS(A−X)

Fig. 1. Emission spectra of CS(A−X) produced from the (a) Kr(3P2)/CS2 and (b) Ar(3P2)/CS2
reactions.

10

Rovibrational Distribution of CS(A) Produced by Collisions of Kr(3P2) with CS2 in the Flowing Afterglow

emission produced from the Ar(3P2)/CS2
reaction is shown in Fig. 1b. Although the sameCS(A−X) emission from 𝑣𝑣 ′ = 0−5 levels isobserved as reported previously,8-10) spectralfeatures are different from those in the
Kr(3P2)/CS2 reaction. In the case of theAr(3P2)/CS2 reaction, CS(A) radicals are morevibrationally excited, so that progressions fromhigh 𝑣𝑣 ′ levels are partially overlapped withthose from low 𝑣𝑣 ′ levels. For example, weak(6,3), (7,4), and (8,5) bands appear on the blue
side of the (2,0), (3,1), and (4,2) bands, andweak (6,4), (7,5), (8,6), and (9,7) bands areobserved on the red side of the (1,0), (2,1), (3.2),and (4,3) bands, respectively, as shown in red
color in Fig. 1b. Therefore, precise
measurements of relative intensities of eachband are difficult without spectral simulation.
On the other hand, CS(A−X) emission fromhigh 𝑣𝑣 ′ levels in the Kr(3P2)/CS2 reaction ismuch weaker than that in the Ar(3P2)/CS2
reaction. Therefore, more reliable intensity
distribution of CS(A−X) emission from low
vibrational levels can be obtained in the
Kr(3P2)/CS2 reaction.
In general, the band intensity (photons s-1) ofa transition from a (𝑣𝑣 ′ , 𝐽𝐽′ ) level to a (𝑣𝑣", 𝐽𝐽")
level is expressed as
𝐼𝐼𝑣𝑣 ′ 𝐽𝐽′ 𝑣𝑣 ′′ 𝐽𝐽′′ ∝ 𝑁𝑁𝑣𝑣 ′ 𝐽𝐽′ 𝑅𝑅𝑅𝑅 2 ( 𝑟𝑟̄ 𝑣𝑣 ′ 𝑣𝑣 ′′ )𝑞𝑞𝑣𝑣 ′ 𝑣𝑣 ′′ 𝜈𝜈𝑣𝑣3′ 𝐽𝐽′ 𝑣𝑣 ′′ 𝐽𝐽′′ 𝑆𝑆𝐽𝐽′ 𝐽𝐽′′ �𝑔𝑔𝐽𝐽′ , (8)where 𝑁𝑁𝑣𝑣′ 𝐽𝐽′ is the rotational population in a
𝑅𝑅𝑅𝑅( 𝑟𝑟̄ 𝑣𝑣′ 𝑣𝑣′′ ) the
given vibrational level 𝑣𝑣 ′ ,electronic transition moment, 𝑞𝑞𝑣𝑣′ 𝑣𝑣′′ the FCF,𝜈𝜈𝑣𝑣′ 𝐽𝐽′𝑣𝑣′′ 𝐽𝐽′′ the transition frequency, 𝑆𝑆𝐽𝐽′ 𝐽𝐽′′ therotational line strength, and 𝑔𝑔𝐽𝐽′ = 2𝐽𝐽′ + 1.20)
The dependence of electronic transition
moment on r-centroid, 𝑅𝑅𝑅𝑅( 𝑟𝑟̄ 𝑣𝑣′ 𝑣𝑣′′ ) , is obtained
from the relation for a (𝑣𝑣 ′ , 𝑣𝑣") band:
𝑅𝑅𝑅𝑅( 𝑟𝑟̄ 𝑣𝑣′ 𝑣𝑣′′ ) ∝ [𝐼𝐼𝑣𝑣′ 𝑣𝑣′′ /𝑞𝑞𝑣𝑣′𝑣𝑣′′ 𝜈𝜈𝑣𝑣3′ 𝑣𝑣′′ ]1/2

(9)

Data from individual 𝑣𝑣" -progressions are
scaled by Fraser’s method21) to account for thedifferent populations among the upper statevibrational levels. Coxon et al.1) determined the
𝑅𝑅𝑅𝑅( 𝑟𝑟̄ 𝑣𝑣′ 𝑣𝑣′′ ) function from the intensity
distributions of 𝑣𝑣 ′ =0−4 𝑣𝑣" -progressions ofCS(A−X) emission in the He afterglow. CS(A)radicals
resultingfromtheCS2+/erecombination reaction (3) in the He afterglow
are more vibrationally excited than that in the
Kr(3P2)/CS2 reaction, as in the case of theAr(3P2)/CS2 reaction. Therefore, there was alarge variation in their data with respect to thefitting line probably due to heavy overlappingof high 𝑣𝑣 ′ 𝑣𝑣" -progressions with low 𝑣𝑣 ′ 𝑣𝑣" -r (Å)
Fig. 2. Dependence of electronic transition
moment of the CS(A−X) transition on
r-centroid.
progressions. In addition, their RKR FCF andr-centroid values were calculated using old
spectroscopic data.22) These provide large
uncertainty in the estimation of 𝑅𝑅𝑅𝑅( 𝑟𝑟̄ 𝑣𝑣′ 𝑣𝑣′′ )values for transitions with small FCFs.
We calculated RKR FCFs and r-centroids
using more reliable spectroscopic data reported
by Bergeman and Cossart.23) Results obtained
were in reasonable agreement with theirreported
data
calculated
using
RKR
potentials.23) Figure 2 shows the dependence ofelectronic transition moment on r-centroid,obtained from 𝑣𝑣 ′ = 1−4 𝑣𝑣" -progressions ofCS(A−X) emission in the Kr(3P2)/CS2 reaction.
It should be noted that variation in our datawith respect to the fitting line is greatly
reduced in comparison with the previous dataof Coxon et al.1) The following linear fitting
curve was obtained:
𝑅𝑅𝑅𝑅( 𝑟𝑟̄ 𝑣𝑣′ 𝑣𝑣′′ ) = 𝐶𝐶(1 − 0.35𝑟𝑟̄ 𝑣𝑣′ 𝑣𝑣′′ ).

(10)

The slope of Eq. (10) is slightly smaller than
0.40 reported by Coxon et al.1) It is muchsmaller than 0.465 obtained by Mahon et al.24)
from laser-induced fluorescence measurements.
We used Eq. (10) for the estimation of
𝑅𝑅𝑅𝑅( 𝑟𝑟̄ 𝑣𝑣′ 𝑣𝑣′′ ) values in Eq. (8).
3.2
Rovibrational distribution of CS(A)produced from the Kr(3P2)/CS2 reaction

Rovibrational distribution of CS(A) in the
Kr(3P2)/CS2 reaction was determined by acomputer simulation of emission spectrum

令和 6 年度

九州大学大学院総合理工学報告第 46 巻第1号

11

Fig. 3. (a) observed and (b) simulated emission spectra of CS(A−X) produced fromthe Kr(3P2)/CS2 reaction.
because rotational structure was not resolvedin the present optical resolution. The rotationalline strength 𝑆𝑆𝐽𝐽′ 𝐽𝐽′′ in Eq. (8) was deduced fromthe formula given by Kovács.25) A Gaussian slit
function was convoluted into rotational lines tocalculate the spectral envelope.
Richards and Setser26) studied the formationof CS(A1Π,a3Π) by the N2(A3Σu+)/CS reaction in
the Ar FA and found that variation of the Ar
pressure from 1.9 to 8 Torr showed nosignificant change in the CS(A−X) spectrum.
Therefore, they concluded that collisional
relaxation by collisions with buffer Ar gas
within radiative lifetimes of 185−255 ns is
insignificant and vibrational distribution ofCS(A) obtained at an Ar pressure of 2.9 Torrcan be taken as the nascent distribution. In thepresent experiment, Ar gas pressure was 0.1
Torr, which was much lower than theirexperiment. It was therefore concluded thatrovibrational distribution of CS(A) obtained
from the Kr(3P2)/CS2 reaction in this study
reflects nascent distribution.
In Figs. 3a and 3b are shown the observed
and best fit spectra of the CS(A−X) band
obtained assuming single Boltzmann rotational
distributions for each 𝑣𝑣 ′ level. The 𝑁𝑁𝑣𝑣′ values
and rotational temperatures of CS(A:𝑣𝑣 ′ = 0−5)
in the Kr(3P2)/CS2 reaction obtained fromspectral simulation are given in Table 1
together with corresponding 𝑃𝑃𝑣𝑣′ values
evaluated from Eq. (7). In Table 1, the most

Table 1.
Vibrational population, relative vibrational formation rate, and rotationaltemperatures of CS(A:𝑣𝑣 ′ =0−6) produced from the Kr(3P2)/CS2 and Ar(3P2)/CS2 reactions and
VUV photoexciation at 123.6 nm (10.03 eV). Two-body and three-body prior distributions in the
Kr(3P2)/CS2 reaction are also shown.
Kr(3P2)9.92 eVThis work

Ar(3P2)
11.55 eV
Ref. 10

𝑃𝑃o𝑣𝑣′

𝑃𝑃o𝑣𝑣′

Two-body

Three-body

VUV
10.03 eV
Ref. 16

𝑁𝑁𝑣𝑣′

𝑃𝑃𝑣𝑣′

𝑇𝑇𝑅𝑅 /K

𝑁𝑁𝑣𝑣′

𝑣𝑣′=0

1.00

1.00

1.00

1.00

𝑇𝑇𝑅𝑅 /K
2300

1.00

1.00

10000±300

1.00

1.00

𝑣𝑣′=1 1.14

0.94

0.74

0.54

2000

1.69

1.39

9000±300

0.79

0.65

0.77

0.65

0.51

0.26

1800

1.26

1.06

8100±300

0.63

0.53

𝑣𝑣′=3

0.51

0.41

0.31

0.10

1500

0.63

0.51

7200±300

0.49

0.39

0.24

0.19

0.15

0.023

1400

0.50

0.39

6400±300

0.43

0.34

𝑣𝑣′=5 0.11

0.08

0.04

0.002

1200

0.44

0.32

5600±30

0.26

0.19

𝑣𝑣′

𝑣𝑣′=2

𝑣𝑣′=4

𝑣𝑣′=6

𝑁𝑁𝑣𝑣′

𝑃𝑃𝑣𝑣′

0.10

𝑃𝑃𝑣𝑣′

12

Rovibrational Distribution of CS(A) Produced by Collisions of Kr(3P2) with CS2 in the Flowing Afterglow

reliable 𝑁𝑁𝑣𝑣′ and 𝑃𝑃𝑣𝑣′ data for the Ar(3P2)/CS2
reaction10) and VUV excitation at 123.6 nm16)
are also given for comparison. In the VUVexcitation, 𝑁𝑁𝑣𝑣′ values were measured for the𝑣𝑣 ′ = 0−6 levels. To the best of our knowledge,
radiative lifetime of 𝑣𝑣 ′ = 6 has not been known,so that only 𝑁𝑁𝑣𝑣′ value is shown for VUV data.
Figure 4 shows 𝑃𝑃𝑣𝑣′ distributions in the
Kr(3P2)/CS2 and Ar(3P2)/CS2 reactions and VUVexcitation at 123.6 nm. Results shown in Table
1 and Fig. 4 indicate that CS(A) in the Kr(3P2)
reaction is less vibrationally excited than thatin the Ar(3P2) reaction. The rotationaltemperatures of CS(A) in the Kr(3P2) reaction
are lower those in the Ar(3P2) reaction by
factors of 4.3−4.8. The vibrational distributionof CS(A: 𝑣𝑣 ′ = 1−3) in the Kr(3P2) reaction ishigher than that of VUV excitation at 10.03 eV,
whereas that of CS(A:𝑣𝑣 ′ = 4,5) in the Kr(3P2)
reaction is lower than the VUV distribution.
The difference between the Kr(3P2) reaction
and VUV excitation with a similar excitationenergy is smaller than that between the Kr(3P2)and Ar(3P2) reactions.
Total available energies, Etot, given in Table 2,
were estimated from the relation ∆𝐻𝐻0𝑜𝑜 +(5/2)RT at 300 K for the reactions:
Kr(3P2) + CS2→ CS(A:𝑣𝑣 ′ =0) + S(3P2) + 0.65 eV

Ar(3P2) + CS2→ CS(A:𝑣𝑣 ′ =0) + S(3P2) + 2.28 eV

(11)
(12)

Kr*

1.2

Pv' of CS(A: v' = 0-5)hν (123.6 nm: 10.03 eV) + CS2→ CS(A:𝑣𝑣 ′ =0) + S(3P2) + 0.76 eV< E v > = ∑𝑣𝑣′ 𝑃𝑃𝑣𝑣′ 𝐸𝐸𝑣𝑣′ / ∑𝑣𝑣′ 𝐸𝐸𝑣𝑣′ ,< f v > = < 𝐸𝐸𝑣𝑣 >/𝐸𝐸𝑡𝑡𝑡𝑡𝑡𝑡 ,VUV (123.6 nm)

0.8
0.6
0.4
0.2

0

1

2

3

4

(14)
(15)
(16)

< f r > = < 𝐸𝐸𝑟𝑟 >/𝐸𝐸𝑡𝑡𝑡𝑡𝑡𝑡 .

(17)< E t > = Etot – (< E v > + < E r > ),< f t > = < E t > /Etot.

(18)
(19)

From the <E v > + <E r > value, the averagerelative translational energy of CS(A) + S and
its fraction to total available energy, <E t > and< f t > , respectively, were evaluated from therelations:

Ar*

1.0

(13)

In the evaluation of ∆𝐻𝐻0𝑜𝑜 values, thedissociation energy of D(CS–S)=4.463 eV and
excitation energy of CS(X:𝑣𝑣 ′′ =0→A:𝑣𝑣 ′ =0)=4.81
eV were obtained from reported data.17,27) The
Etot value of the Kr(3P2) reaction is decreased toabout 1/3 in comparison with that of the Ar(3P2)
reaction. This will be a major reason for the
lower vibrational and rotational excitation in
the Kr(3P2) reaction than that in the Ar(3P2)
reaction. On the other hand, difference in the
Etot value between the Kr(3P2) reaction and VUVexcitation is small (0.07 eV). This small
difference will be a major reason for the small
difference in the vibrational distribution
between the two excitation methods.
Fromtheobserved
rovibrational
distributions of CS(A) and Etot value, weestimated the average vibrational androtational energies of CS(A), denoted as < E v >and <E r > , and the average yields of total
available energy into these degrees of freedom,denoted as < f v > and < f r > , respectively fromthe relations:< E r > = 𝑘𝑘 ∑𝑣𝑣′ 𝑃𝑃𝑣𝑣′ 𝑇𝑇𝑣𝑣′ / ∑𝑣𝑣′ 𝑃𝑃𝑣𝑣′ ,

1.4

0.0

On the other hand, the Etot value in VUVphotodissociation (13) was obtained from therelation ∆𝐻𝐻0𝑜𝑜 + RT at 300 K.

5v' of CS(A)Fig. 4. Vibrational distribution of CS(A)produced by Kr(3P2), Ar(3P2),10) and VUVphotoexcitation (123.6 nm).16)

The < E v > , < E r > , <Et>, < f v > , < f r > , and < f t >values thus obtained for the Kr(3P2) reaction
are summarized in Table 2 along with thereported data of the Ar(3P2) reaction and VUVphotoexcitation (10.03 eV). For VUV excitation,
only <E v > and < f v > values obtained from
𝑃𝑃𝑣𝑣′ ( 𝑣𝑣 ′ = 0−5) values are shown because
rotational distributions of each vibrational
state were not determined. The < f v > value ofthe Kr(3P2) reaction is 2.7 times larger than令和 6 年度

九州大学大学院総合理工学報告

Table 2. Average vibrational and rotationalenergies deposited into CS(A) and relativetranslational energy deposited into CS(A) + S,
and average fractions of above energies tototal available energies in the Kr(3P2)/CS2 andAr(3P2)/CS2 reactions and VUV (10.03 eV)photoexcitation.
Kr(3P2)Ar(3P2)This work

Ref. 10

Etot (eV)0.71 eV

2.34 eV<𝐸𝐸𝑣𝑣 >

0.18 eV0.22 eV<𝐸𝐸𝑟𝑟 >

0.17 eV

0.72 eV<𝐸𝐸𝑡𝑡 >

0.36 eV

1.40 eV<𝑓𝑓𝑣𝑣 >

25%

9.4%

<𝑓𝑓𝑟𝑟 >

24%

31%

<𝑓𝑓𝑡𝑡 >

51%

60%

VUV
123.6 nmRef. 160.78 eV
0.21 eV27%

3.2 The reaction dynamics for the formationof CS(A) in the Kr(3P2)/CS2 reaction
3.2.1

Statistical models

The formation dynamics of CS(A) from theKr(3P2)/CS2 reaction is discussed assuming
two-body
andthree-bodydissociation
mechanisms, which have been used in theformation of OH(A2Σ+) from the Ar(3P0,2)/H2O
reaction.28)(a) Two-body dissociation process throughresonant excitation transfer:
Kr* + CS2 → CS2* + Kr,CS2* → CS(A) + S,

13

Kr* + CS2 → KrCS2*,
KrCS2* → CS(A) + S + Kr.

(22)

In processes (a), energy is resonantly
transferred from Kr* to CS2, and then CS2*
dissociates into CS(A) + S. In process (b) KrCS*
intermediate is formed through Kr+CS2- ionpair. In process (c), CS(A) radicals are produced
through three-body dissociation of KrCS2*
complex. The electron affinity of CS2 has beenmeasured as 0.5525±0.0013 eV,29) so that stable
CS2- anion can be formed. Whereas the neutral
moleculeislinear,the
CS2(X1Σg+)corresponding anion, CS2-(X2A1), is bent ∠SCS
≈145o,30,31) leading to poor FC overlap in thevertical CS2(X1Σg+) → CS2-(X2A1) electron
attachment process. Thus transfer fromentrance V (Kr*, CS2) potential to V (Kr+, CS2-)
ion-pair one will be inefficient. We therefore
excluded process (b) through Kr+CS2- ion-paircomplex from the above three possible reaction
processes.
Statistical vibrational and rotational
distributions were calculated for two processes(a) and (c). According to a simple statisticaltheory,32-35) the probability of forming a
CS (A: 𝑣𝑣 ′ , 𝐽𝐽′ ) rovibrational level throughprocesses (a) and (c) is, respectively, expressedby
1/2

𝑃𝑃𝑣𝑣𝑜𝑜′ 𝐽𝐽′ ∝ (2𝐽𝐽′ + 1)�𝐸𝐸tot − 𝐸𝐸𝑣𝑣CS ∗ �
3/2

𝑃𝑃𝑣𝑣𝑜𝑜′ ∝ �𝐸𝐸tot − 𝐸𝐸𝑣𝑣CS ∗ �

(23a)

,

(23b)

,

1.0
Obs.

0.8

Process (a)Process (c)

0.6
0.4
0.2

(20)

(b) Two-body dissociation process throughion-pair intermediate:
Kr* + CS2 → Kr+CS2- → KrCS* + S,
KrCS* → CS(A) + Kr,

第1号(c) Three-body dissociation process throughresonant excitation transfer:

Pv' of CS(A: v' = 0-5)that of the Ar(3P2) reaction, whereas the < f r >value of the Kr(3P2) reaction is 23% smaller
than that of the Ar(3P2) reaction. The < f v > +< f r > value of the Kr(3P2) reaction is 21% larger
than that of the Ar(3P2) reaction. This result
indicates that deposition of excess energy into
internal energy is more favorable in the Kr(3P2)
reaction, whereas that into translationalenergy is more favorable in the Ar(3P2) reaction.
The < f v > value in the Kr(3P2) reaction wascomparable with that in VUV excitation.

第 46 巻

(21)

0.0

0

1

2

3

4

5

v' of CS(A)Fig. 5. Observed and two-body and threebody prior vibrational distributions in the
Kr(3P2)/CS2 reaction.

14
𝑃

Rovibrational Distribution of CS(A) Produced by Collisions of Kr(3P2) with CS2 in the Flowing Afterglow

∝ 2𝐽′

1 𝐸

𝑃′∝ 𝐸

𝐸

∗

𝐸

∗

(24a)

,

(24b)

.

The
prior
vibrationalandrotational
distributions of CS(A: 𝑣 =0–5) for processes (a)and (c) are compared with the observed ones in
Figs. 5 and 6a–6f, and Table 1. Both two-body(a) v’ =0

0.8

0.6

0.4

Obs.
Process (a)Process (c)0.2(d) v’=3

1.0
Rotational distributions of CS(A:v'=3)

1.0
Rotational distributions of CS(A:v'=0)

and three-body prior vibrational distributionsof CS(A: 𝑣 =0–5) predict lower distributions
than observed one. The observed rotationaltemperature decreases from 2300 K to 1200 K
with increasing 𝑣 from 0 to 5. Therefore, peak
population slowly decreases from 𝐽 =32 to 30,
28, 26, 25, and 23 with increasing 𝑣 from 0 to
5, respectively. Peaks of two-body and three-

0.0

0.8
Obs.
Process (a)Process (c)

0.6

0.4

0.2

0.0

0

20

40

60

80

100

0

20

J ' of CS(A : v' = 0)(b) v’=1

0.8

0.6

0.4

Obs.
Process (a)Process (c)

0.2

0.0

100

Obs.
Process (a)Process (c)

0.8

0.6

0.4

0.2

0.0
0

20

40
60
J ' of CS(A : v' = 1)

80

100

0

Rotational distributions of CS(A:v'=5)

0.6

Obs.
Process (a)Process (c)

0.2

0.0
0

20

40
60
J ' of CS(A : v' = 4)

80

100

1.0

0.8

0.4

20

(f) v’=5(c) v’=2

1.0
Rotational distributions of CS(A:v'=2)80(e) v’=4

1.0
Rotational distributions of CS(A:v'=4)Rotational distributions of CS(A:v'=1)

1.0

40
60
J ' of CS(A : v' = 3)4060
J ' of CS(A : v' = 2)

80

100

Obs.
Process (a)Process (c)

0.8

0.6

0.4

0.2

0.0
0

20

40

60

80

100

J' of CS(A : v' = 5)

Fig. 6. Observed and statistical prior rotational distributions of CS(A: 𝑣 =0−5) in the
Kr(3P2)/CS2 reaction.

令和 6 年度

九州大学大学院総合理工学報告

body prior rotational distributions decrease
more rapidly from 𝐽𝐽′ =49 and 38 for 𝑣𝑣 ′ =0 to
𝐽𝐽′ =45 and 34 for 𝑣𝑣 ′ =1, 𝐽𝐽′ =40 and 30 for 𝑣𝑣 ′ =2,
𝐽𝐽′ =34 and 26 for 𝑣𝑣 ′ =3, 𝐽𝐽′ =27 and 20 for 𝑣𝑣 ′ =4,
and 𝐽𝐽′ =17 and 13 for 𝑣𝑣 ′ =5, respectively. These
results indicate that observed vibrational androtational distributions cannot be explained bytwo- and three-body statistical prior models.
On the basis of above findings, CS(A) radicals
are not formed via long lived intermediates
where excess energy is distributed statistically
before predissociation.
3.2.2

Dissociation pathways

Based on extensive experimental studies onenergy-transfer reactions from metastable
Ar(3P2), Kr(3P2), Xe(3P2) atoms to such diatomic
molecules as N2 and CO, the formation of nearresonant states via E-E transfer is major exit
channel in most cases, because conversion ofinternal energy of metastable atoms to relativetranslational energy of products (E-T transfer)is unfavorable.19.36-50) It is therefore reasonable
to assume that CS(A1Π) + S(3P2) products result
from near-resonant E-E transfer followed by
predissociation of CS2** states in the
Kr(3P2)/CS2 and Ar(3P2)/CS2 reactions.

17

CS+ + S

~
B2 +
u

14.5

~
A2

Potential energy (eV)u

CS+ + S

CS2+

12.7
11.55

Ar(3P2)

~

X2g
10.07
9.92
9.27

3Σ+, 3Σ-, 3Π, 3∆

Kr(3P2)
CS(A1Π) + S(3P2)

CS + S

4.0

CS2
CS2

X1g+

Fig. 7. Potential energy curves of bound� 2Πu, B� 2Σu+)
X 2Πg, A
CS2(X1Σg+) and CS2+( �1
3states and repulsive CS(A Π) + S( P2) statesand energies of Ar(3P2) and Kr(3P2).

第 46 巻第1号

15

Figure 7 shows potential energy diagram of� 2Πu, B� 2Πg, A� 2Σu+), repulsive
CS2(X1Σg+), CS2+(XCS(A1Π) + S(3P2) potentials, and Kr(3P2) andAr(3P2) atoms. From the correlation diagram,high-energy 3Σ+, 3Σ-, 3Π, and 3∆ states of CS2*
arise from the CS(A1Π) + S(3P) dissociation
limit.51) It should be noted that the CS(A1Π) +S(3P2) dissociation limit is only 0.65 eV below
the energy of Kr(3P2), and the energy of Kr(3P2)
�) ionic state.
is 0.15 eV below the ground CS2+(X
Since no ionic states can be formed in the
Kr(3P2)/CS2 reaction, only high-energy neutral
states can be precursor states of CS(A1Π) +S(3P2) fragments. In the Ar(3P2)/CS2 reaction,
the energy of Ar(3P2) is 1.48 eV higher than the� ) state, so that the CS(A1Π) + S(3P2)
CS2+( X
fragments are expected to be formed via nearresonant superexcited CS2** states.52)
Since spin-orbit interaction by the presenceof two heavy S atoms is large for CS2,
intersystem crossing between singlet andtriplet states will occur efficiently. Therefore,CS(A1Π) + S(3P2) fragments, which correlatewith triplet CS2* states, are formed under VUVphotoexciation.15-18) This indicates that spinconservation rule is violated for CS2 underphotoexcitation. The violation of spinconservation rule is expected to be held in theRg(3P2) (Rg=Kr, Ar) excitation, where triplet
states are favored according to this rule. Bothsinglet and triplet states can be formed under
VUV and Rg(3P2) excitation. It is therefore
reasonable to discuss possible precursor CS2**
states in the Rg(3P2) excitation from reported
VUV absorption, fluorescence cross-section,and fluorescence quantum yield data of
CS2.17,18) Okabe17) measured absorption andCS(A−X) fluorescence excitation spectra of CS2
in the 120−135 nm region. In the excitation
spectrum, a broad excitation peak with manyfine structures were observed in the 120−134
nm region and some of their peak positions
agreed with Rydberg series I and II given by
Tanaka et al.53) Day et al.18) measured
absorption and fluorescence (190−300 and
190−800 nm) cross sections in a wider
excitation wavelength region of 106−152 nm.
Absorption and fluorescence cross sections in
the 120−135 nm region agreed well withprevious data of Okabe.17)
Figure 8 shows the dependence of 190−300
nm fluorescence cross section on the
wavelength in the 121−140 nm (8.86−10.3 eV)region reported by Day et al.,18) where energies
of Kr(3P2), CS(A) + S(3P2) dissociation limit, andeight typical Rydberg states in this wavelength

16

Rovibrational Distribution of CS(A) Produced by Collisions of Kr(3P2) with CS2 in the Flowing Afterglow
Energy (eV)
9.92
Kr(3P2)(5/2)RT

6pπu
6pσu

π → ns GK

9

0
121

125

π → nsδ=1.03π → nsδ=1.56

3

130

135

5

Ⅰ

3

5

CS2+(2Π3/2)

π → nsδ=1.9755
2.5

δ=1.236

7
CS2+(2Π1/2)

π → ns

5

7

RMSM

8.86

9.18
CS(A1Π) + S(3P2)

9.99 eV 8pπu
9pσuFluorescence cross section (10-18 cm2)

Energy (eV)

9.54

Ⅱ

TJL

140

Wavelength (nm)Fig. 8. Dependence of fluorescence crosssection of 190–300 nm emission on the
wavelength.18) Rydberg series reported by
Tanaka et al. (TJL: Ref. 53), Rabalais et al.
(RMSM: Ref. 54), and Greening and King (GK:
Ref. 55). Energies of CS(A1Π) + S(3P2)
dissociation limit and Kr(3P2) are also shown.
region53-55) are shown. The total energy ofreactant Kr(3P2) + CS2 system is 9.99 eV taking
account of (5/2)RT at 300 K. Although manyother Rydberg states were identified in thiswavelength region,56-58) they are omitted in Fig.
8 for the sake of clarity. In this wavelength
region, many Rydberg series converging to the
X 2Π3/2) and CS2+( �X 2Π1/2) ionicground CS2+( �states and those to excited CS2+ states areoverlapped with each other. Some fluorescencecross-section peaks coincide with such Rydberg
states. This indicates that CS(A) is formed
through predissociation of Rydberg states in
the 121−134 nm (9.25−10.25 eV) region. Since
autoionization does not compete withpredissociation in Rydberg states below theionization potential, quantum yield for the
production of 190−300 nm fluorescence in the123−127 nm (9.76−10.07 eV) region isrelatively high (≈7%).18) The near-resonant
Rydberg states in the 9.25−9.99 eV region(124−127 nm), especially those in the 9.76−9.99
eV region, will be major precursor CS2** statesin the Kr(3P2)/CS2 reaction.
Figure 9 shows the dependence offluorescence cross section on the wavelength in
the 106−120 nm (10.3−11.7 eV) region18) andthe energy of Ar(3P2). The total energy of thereactant Ar(3P2) + CS2 system is 11.61 eV
including (5/2)RT at 300 K. In the Ar(3P2)/CS2
reaction, the most probable precursor states
are doublet n = 4 nsσ-type Rydberg state Ⅲ

Fluorescence cross section (10-18 cm2)

10.25

10.78

10.33

115
110
Wavelength (nm)

120

11.27

11.70

n=4Ⅲ
ns

11.61 eV
Ar(3P2)50106(5/2)RT

Fig. 9. Dependence of fluorescence crosssection of 190–300 nm emission on the
wavelength.18) Green dots are unidentified
structures.
� ) state and weak
converging to the CS2+( Bfeatures degraded to shorter wavelength region(green dot color bands in Fig. 9). Strong doublet
n = 4 Rydberg state Ⅲ bands, which wereoriginally assigned to n = 2 Rydberg state Ⅲ
by Tanaka et al.,53) were revised as n = 4 nsσtype Rydberg state Ⅲ by Larzilliere andDamany.59) Weak additional features in the
108−111 nm region (green dot bands in Fig. 9)
were often observed in VUV absorption
spectra.18,53,56,59) These features show a clear
vibrational progression having an average
spacing of ≈0.065 eV (≈530 cm-1). They areprobably associated with autoionization
features from various vibrational states of ahigh lying Rydberg state having a separation
close to ν1 mode.56) If these features become
precursor CS2** states, excitation of ν1 mode ofCS2** contributes to vibrational excitation ofCS(A) after predissociation to some extent.
In the Ar(3P2)/CS2 reaction, 0.94 eV isreleased as rovibrational energies of CS(A), as
shown in Table 2. It is therefore highly likelythat precursor state is located at least 0.94 eVhigher than the CS(A) + S dissociation limit.
Such a state with an excitation energy higher
than 10.21 eV is higher than the energy of� ) (10.07 eV). Therefore, superexcited
CS2+( X� ) state must be
states above the CS2+( Xdominantly responsible for the formation ofCS(A).
Day et al.18) reported that the fluorescencecross section of 190−300 nm fluorescence ishigh in the 109.5−111.5 nm (11.12−11.32 eV)region and its quantum yield is about 3.5%. It
is therefore expected that near-resonant令和 6 年度

九州大学大学院総合理工学報告

Rydberg states in the 108–113 nm (10.97–11.48
eV) region, especially those in the 11.12−11.32
eV region, will be major precursor states in theAr(3P2)/CS2 reaction. Based on this fact, CS(A)radicalsaredominantly
formedbypredissociation of these superexcited states,
where predissociation and autoionization to�) compete with each other.
CS2+(X
The above conclusion for the precursor CS2**
states in the Ar(3P2)/CS2 reaction isinconsistent with that of Wu.9) He reported that
CS(A) originates from predissociation of the
Rydberg state converging into the ground stateof CS2+ below the ionization limit, via a very
steep repulsive potential curve, because
fluorescence efficiencies of CS2 become quite
small below the wavelength corresponding to
the ionization potential of CS2 based on theexperimental data of Okabe17) in the 120–135
nm region. However, VUV excitation data by
Day et al.18) in a wider excitation wavelength
range of 106–152 nm demonstrated thatfluorescence cross section of the 190–300 nm
emission has additional peaks in the 108–113
�) state (see Fig. 9).
nm region above the CS2+(X
We therefore concluded that near-resonant
CS2** states in the 108–113 nm region are
more important precursor states than nonresonant Rydberg states in the 121–134 nm
region.
De Vries et al.60) studied the Ar(3P2)/CS2
reaction using a beam apparatus. They foundthat the cross section for dissociative excitation
giving CS(A) is largest when the CS2 bond isperpendicular to the relative velocity vector.
According to their proposed reaction dynamics,
CS(A) is formed via one or more surface
crossings.
The
most likely
formationmechanism is by crossing of entrance
V [Ar(3P2), CS2] potential to attractive
V (Ar+, CS2-) ion-pair potential followed byanother crossing to a high lying V (Ar, CS2**)
neutral potential, which dissociates to Ar +CS2** Rydberg state. Assuming that thethreshold for CS(A: 𝑣𝑣 ′ = 0) is the same as inphotodissociation,17) the CS(A:𝑣𝑣 ′ = 6) level is at�) level
10.02 eV, which is just below the CS2+(Xof 10.07 eV. Thus they proposed that CS(A) is
formed via crossover from V (Ar+, CS2-) toV (Ar, CS2**) below the ionization level. As
discussed above, the most probable precursor
states will be superexcited CS2** states above
the ionization level. Therefore, predissociationof CS2** Rydberg states below the ionizationlevel will be unimportant for the formation ofCS(A) in the Ar(3P2)/CS2 reaction.

第 46 巻第1号

17

We proposed the most probable precursor
CS2** Rydberg states in the Kr(3P2)/CS2 andAr(3P2)/CS2 reactions. As shown in Fig. 7, theprecursor repulsive CS(A1Π) + S(3P2) curve in
the Kr(3P2)/CS2 reaction is less steep than thatin the Ar(3P2)/CS2 reaction. After near-resonant
E-E transfer from V [Kr(3P2), CS2] toV (Kr, CS2**), the V (Kr, CS2**) potentials crosswith the gently repulsive CS(A1Π) + S(3P2)
potential at lower energy region below theionization level. On the other hand, in theAr(3P2)/CS2 reaction, after similar nearresonant E-E transfer, V (Ar, CS2**) potentials
cross with the highly repulsive CS(A1Π) +S(3P2) potential at higher energy region above
the ionization level. This is a major reason why
the <ft> value in the Kr(3P2)/CS2 reaction issmaller than that in the Ar(3P2)/CS2 reaction,
whereas the <fv> + <fr> value in the Kr(3P2)/CS2
reaction is higher than that in the Ar(3P2)/CS2
reaction.

4.

Summary and Conclusion

CS(A1Π−X1Σ+) emission from 𝑣𝑣 ′ = 0–5 wasobserved by the Kr(3P2)/CS2 reaction in the FA.
The dependence of electronic transition
moment on r-centroid was determined from the𝑣𝑣 ′ = 1−4 𝑣𝑣"-progressions of CS(A−X) emission.
The vibrational populations of CS(A:𝑣𝑣 ′ = 0–5),
𝑁𝑁𝑣𝑣′ , and the relative vibrational formation ratesof CS(A: 𝑣𝑣 ′ = 0–5), 𝑃𝑃𝑣𝑣′ , were estimated. The
rotational distribution of CS(A: 𝑣𝑣 ′ = 0–5) was
expressed by single Boltzmann rotationaltemperatures (𝑇𝑇𝑅𝑅 ) of 1400–2300 K. By using theobserved 𝑃𝑃𝑣𝑣′ and 𝑇𝑇𝑅𝑅 data, the < f v > , < f r > , and< f t > values were determined to be 25%, 24%,
and 51%, respectively. The observed 𝑃𝑃𝑣𝑣′ and
𝑇𝑇𝑅𝑅 data of CS(A:𝑣𝑣 ′ = 0–5) were compared withstatistical prior vibrational and rotational
distributions. The reaction dynamics could not
be explained by simple statistical models. It
was concluded that major precursor statesleading to CS(A) + S(3P2) in the Kr(3P2)/CS2 andAr(3P2)/CS2 reactions are near-resonant
Rydberg states in the 9.25−9.99 eV and 10.97–
11.48 eV region, respectively. Curve crossings
between low-energy Rydberg states with gently
repulsive CS(A) + S(3P2) curve provide a lower< f t > value and a higher < f v > + < f r > value inthe Kr(3P2)/CS2 reaction in comparison withthose in the Ar(3P2)/CS2 reaction.
Acknowledgments
The authors acknowledge Prof. Kenji Furuya
of Kyushu University for his careful reading of
our manuscript. We would also like to thank18

Rovibrational Distribution of CS(A) Produced by Collisions of Kr(3P2) with CS2 in the Flowing Afterglow

Prof. M. N. R. Ashfold of University of Bristol
for sending us a copy of Ref. 16. This work was
supported by the Mitsubishi foundation (1996).
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