Photoionization dynamics in CS fragmented from CS2 studied by high-resolution photoelectron spectroscopy

Article abstract of DOI:10.1139/v04-015

The photoionization dynamics of CS have been studied using high-resolution laser photoelectron spectroscopy. The photodissociation of CS₂ at ～308 nm results in highly rotationally excited CS in its X ¹∑⁺ singlet ground state, as well as in rotationally cold CS in the excited a³Π triplet state. The ground-state CS fragments are formed together with sulfur in its ³P, ¹D, and ¹S electronic states; triplet CS is produced in coincidence with ground-state sulfur (³P). In both channels the photoelectron spectra are dominated by Δν = 0 propensity, but transitions involving Δν = 1 and 2 are also observed.

Full text of DOI:10.1139/v04-015

7
44
Photoionization dynamics in CS fragmented from
CS studied by high-resolution photoelectron
2
1
spectroscopy
Anouk M. Rijs, Ellen H.G. Backus, and Cornelis A. de Lange
Abstract: The photoionization dynamics of CS have been studied using high-resolution laser photoelectron spectros-
1
+
copy. The photodissociation of CS at ~308 nm results in highly rotationally excited CS in its X Σ singlet ground
2
3
state, as well as in rotationally cold CS in the excited a Π triplet state. The ground-state CS fragments are formed to-
gether with sulfur in its P, D, and S electronic states; triplet CS is produced in coincidence with ground-state sulfur
P). In both channels the photoelectron spectra are dominated by ∆v = 0 propensity, but transitions involving ∆v = 1
3
1
1
3
(
and 2 are also observed.
Key words: photoelectron spectroscopy, photoionization, photodissociation, excited states, reactive intermediates.
Résumé : On a étudié la dynamique de photoionisation du CS en faisant appel à la spectroscopie photoélectronique la-
ser à haute résolution. La photodissociation du CS à environ 308 nm conduit à la formation de CS fortement excité
2
1
+
d’un point de vue rotationnel, dans son état fondamental singulet X Σ , ainsi que de CS rotationnellement froid dans
3
un état triplet excité a Π. Les fragments CS dans l’état fondamental se forment en même temps que du soufre dans les
3
1
1
états électroniques P, D et S; les quantités de CS à l’état triplet se forment en coïncidence avec le soufre à l’état
3
fondamental ( P). Dans les deux voies, les spectres photoélectroniques sont dominés par la propensité ∆v = 0, mais on
observe aussi des transitions de ∆v = 1 et 2.
Mots clés : spectroscopie photoélectronique, photoionisation, photodissociation, états excités, intermédiaires réactifs.
[
Traduit par la Rédaction] Rijs et al. 749
Introduction
obtained. These rotationally resolved photoelectron spectra
provide information on the photoionization dynamics.
Resonance-enhanced multiphoton ionization, in combina-
tion with kinetic energy resolved photoelectron spectroscopy
In the present work the photodissociation of CS , resulting
2
in CS photofragments, has been studied. The ionization en-
2
+
(
REMPI-PES), has proven to be an excellent and powerful
ergy of CS from its neutral ground state to the lowest X Σ
method to study rotationally resolved photoionization and
photodissociation dynamics of rotationally hot photofragments
ionic state amounts to 11.33 eV (4). The rotational constant
+
–1
of CS in its ionic ground state is only 0.857662 cm (5).
However, when the CS photofragments are formed with suf-
ficient rotational excitation, rotational levels in the ion with
(
1–3). In particular, with REMPI-PES, detailed information
about the spectroscopy and photoionization dynamics of the
intermediate state can be obtained. Fragments formed in a
photofragmentation process are often generated with an ap-
preciable degree of electronic, vibrational, and rotational
excitation. With sufficient rotational excitation, even for
fragments with small rotational constants, the spacings be-
tween excited rotational levels in the ion may exceed the en-
ergy resolution of the magnetic bottle electron spectrometer
used, and rotationally resolved photoelectron spectra can be
+
high J are accessed, and rotationally resolved PES can be
observed.
Carbon disulphide (CS ) has a structure and a photo-
2
dissociation behavior similar to that of the previously stud-
ied N O and OCS (1–3). These molecules all possess a
2
linear ground-state geometry with a 16 valence electron con-
figuration. The absorption spectrum of CS shows many
2
absorption bands between ~100 and 400 nm (6). The photo-
Received 7 June 2003. Published on the NRC Research Press Web site at http://canjchem.nrc.ca on 25 June 2004.
A.M. Rijs. Laboratory for Physical Chemistry, University of Amsterdam, Nieuwe Achtergracht 127–129, 1018 WS Amsterdam, The
Netherlands and Laser Centre and Department of Chemistry, Vrije Universiteit, De Boelelaan 1083, 1081 HV Amsterdam, The
Netherlands.
E.H.G. Backus. Leiden Institute of Chemistry, Leiden University, Einsteinweg 55, P.O. Box 9502, 2300 RA Leiden, The
Netherlands.
2
C.A. de Lange. Laser Centre and Department of Physics, Vrije Universiteit, De Boelelaan 1081, 1081 HV Amsterdam, The
Netherlands and Department of Chemistry, The University, Southampton SO17 1BJ, UK.
1
This article is part of a Special Issue dedicated to the memory of Professor Gerhard Herzberg.
Corresponding author (e-mail: delange@science.uva.nl).
2
Can. J. Chem. 82: 744–749 (2004)
doi: 10.1139/V04-015
© 2004 NRC Canada

Rijs et al.
745
chemistry of CS is strongly dependent on the wavelength of
Table 1. Threshold energies of the product states in the
photodissociation of CS2.
2
photolysis. Absorption of one photon of 193 nm results in
1
+
the production of singlet CS (X Σ ) fragments and sulfur at-
1
3
Pathway
1]
[2]
3]
[4]
CS channel
S channel
Energies (eV)
oms in the singlet or triplet state ( D or P) (7, 8). For
photolysis wavelengths towards the ultraviolet, the produc-
1
+
3
[
CS (X Σ )
S ( P )
4.46
5.61
7.21
7.88
J
3
1
+
1
tion of triplet CS (a Π) becomes more important, and be-
CS (X Σ )
S ( D )
2
1
+
1
tween 140 and 125 nm, the CS fragments are almost
[
CS (X Σ )
S ( S )
0
completely produced in the triplet state (9). CS shows a
3
3
2
CS (a Π)
S ( P )
J
strong absorption band around 340–290 nm. This band has
~
~
~
1
1
1
+
been assigned to the B ← X Σ transition. This B upper
2
g
2
state is bent with an SCS angle of 131° and correlates to the
valence state in the linear configuration (10). One-
photon excitation of CS at ~308 nm (4.03 eV) correlates to
1
Experimental
∆
u
2
~
The experimental setup has been reported in great detail
previously (1). Briefly, the laser system consists of an XeCl
excimer laser (Lumonics HyperEx-460), producing pulsed
radiation with a fixed wavelength of 308 nm and a pulse du-
ration of ~10 ns. The laser pulses are generated with a repe-
tition rate of 30 Hz and have an energy of 200 mJ pulse .
The excimer laser output is used to pump a dye laser
1
the transition to the B state. CS photofragments are formed
2
by the sequential (1+1) absorption of two photons at
~
1
~
308 nm (total energy 8.06 eV) via the B intermediate
2
state to a predissociative excited state lying near 150 nm (6).
This state predissociates, yielding CS photofragments in
combination with S atoms. There are several dissociation
pathways in our energy region that can be accessed, produc-
ing singlet and triplet CS fragments (see Table 1), as fol-
lows:
–1
(
Lumonics HyperDye 500), operating on Rhodamine (band-
–1
width ~0.08 cm ). The dye laser output (about 615 nm) is
frequency-doubled in a Lumonics HyperTrak 1000, using a
KD*P crystal, resulting in 10-ns pulses with a maximum en-
ergy of about 15 mJ and a bandwidth of ~0.2 cm . The laser
light is focused into the ionization region of a magnetic bot-
tle spectrometer by a quartz lens with a focal length of
1
+
3
[
[
[
[
1]
2]
3]
4]
CS → CS (X Σ ) + S ( P )
2
J
–
1
1
+
1
CS → CS (X Σ ) + S ( D )
2
2
1
+
1
CS → CS (X Σ ) + S ( S )
2
0
2
5 mm. The laser pulse intensity is kept low enough to avoid
3
3
nonresonant ionization of the parent compound CS . In the
CS → CS (a Π) + S ( P )
2
2
J
present experiments, the magnetic bottle spectrometer is
used in the electron detection mode for both wavelength
scans and photoelectron spectra and operates with a collec-
tion efficiency of ~50%. Since a time-of-flight method is
used, time windows can be selected to achieve optimum res-
olution. Signal intensities are essentally independent of ki-
netic energies (1).
Dissociation pathways [2], [3], and [4] are spin-allowed
processes from the optically prepared state. The first dissoci-
ation pathway [1] is a spin-forbidden process, which
becomes weakly allowed by the spin–orbit interaction asso-
ciated with the presence of the two sulfur atoms in CS2.
The present paper is concerned with rotationally and
vibrationally resolved laser photoelectron spectroscopy of
CS fragments. At about 308 nm, the CS photofragments can
be produced either in the singlet or the triplet state. The CS
The CS photofragments are generated in situ by two-
photon dissociation of CS (Sigma-Aldrich, HPLC grade).
2
The CS gas sample is effusively introduced into the ioniza-
2
1
+
fragments formed in the X Σ ground state are rotationally
tion chamber through a 13 mm outer diameter Pyrex flow
tube, leading to a pressure in the ionization region of typi-
hot and are studied via a (2+1) ionization scheme using the
1
+
–
3
intermediate B Σ Rydberg state as a stepping-stone. The in-
cally 10 mbar (1 bar = 100 kPa). The photodissociation of
1
+
termediate B Σ Rydberg state represents the lowest member
CS and the subsequent ionization of the CS fragments are
2
2
+
of a Rydberg series converging upon the X Σ ionic ground
performed with the same laser photons of about 308 nm. For
calibration of both the wavelength and the photoelectron ki-
netic energies, well-known resonances of sulfur atoms at
two-photon energies of 64 889.0 and 66 741.6 cm–1 are used
+
state of CS and is located at about 8.04 eV above the CS
1
+
(
X Σ ) ground state (11). Together with the CS fragments
formed in their singlet state, S atoms are also produced.
These sulfur atoms can be formed via dissociation pathways
(
12, 13).
3
[
(
(
1], [2], and [3], resulting in ground- ( P ) and excited-state
J
1
3
1
D , S ) S atoms. Various (2+1) ionization transitions of S
2
0
Results and discussion
1
P , S ) are used for calibration.
J
0
1
+
In addition to ground-state CS (X Σ ) fragments, excited
At 308 nm, the dissociation of CS produces CS in the
2
3
1
+
3
CS fragments can also be formed in the triplet state (a Π)
X Σ ground state or in the a Π triplet state. Figure 1 shows
a two-photon excitation spectrum of CS fragments in the
two-photon energy range 65 000 – 65 170 cm . The spec-
via the dissociation route [4]. The electronically excited trip-
3
–1
let CS (a Π) fragments, which possess low rotational excita-
tion, are studied employing a (1+1) excitation step via the
trum was obtained by monitoring electrons with a kinetic en-
ergy of about 0.75 eV (flight time range of 2840–3000 ns).
These photoelectrons arise from a (2+1) ionization process,
3
+
+
2 +
intermediate CS ( Σ ) state, resulting in CS (X Σ ) ionic
3
fragments. With our photon energies, the CS (a Π) frag-
3
1 +
ments can only be formed together with ground-state S ( P )
starting from the X Σ (v′′ = 1; N′′) electronic ground state
J
1 +
atoms. The appearance energy of the other dissociation
via the intermediate B Σ (v′ = 1; N′) Rydberg state to the
2 + + +
3
1
1
channels of triplet CS (a Π) + S ( D , S ) lies above our
X Σ (v = 1; N ) ionic ground state. The rotationally re-
2
0
two-photon dissociation energy.
solved excitation spectrum shows the rotational distribution
©
2004 NRC Canada

7
46
Can. J. Chem. Vol. 82, 2004
Fig. 1. Rotationally resolved (2+1) REMPI excitation spectrum
Fig. 2. (a) Rotational fit of the measured line positions for the
1
+
1
+
1 +
with electron detection of the Q branch of the B Σ ← ← X Σ
B Σ (v′ = 1) Rydberg state, based on the rotational constants of
1 +
transition of hot CS fragments in the two-photon energy range
the X Σ ground state of CS (v′′ = 1) (17). Results are given in
Table 2; (b) Residual plot, the difference between the experimen-
tal and calculated line positions.
–
1
6
5 000 – 65 170 cm (vacuum energies).
1
+
of the Q branch (∆N = 0) of CS in the B Σ (v′ = 1) state,
extending from N′ = 35 up to N′ = 71. The comb above the
spectrum in Fig. 1 indicates the assignment of the N′ rota-
tional levels.
–
1
1 +
Table 2. Rotational constants (in cm ) for the B Σ (v′ = 1)
Rydberg state of CS (left column), and a comparison with the
literature (14) (central column).
In the absorption step, only the transition from the v′′ = 1
1
+
1 +
level of X Σ to the v′ = 1 level of B Σ is observed. No tran-
1
+
B1Σ+
X1Σ+
B Σ (v′ = 1)
1
+
sitions arising from X Σ for v′′ ≠ 1 were observed. This
unusual situation has to do with the properties of the vibra-
v11
64 952.60(36)
—
—
1
+
tional levels associated with the B Σ state. It is known from
B1
0.85188(24)
0.8520
1.56×10–6
0.811163722
1.337566×10–6
1
+
1.3802(38)×10–6
the literature (14) that the B Σ Rydberg state predissociates,
especially from the v′ = 0 and the v′ = 2 levels. Moreover,
Sapers and Donaldson (15), who studied the rovibrational
D1
1
+
Note: The ground-state rotational constants of CS (X Σ ) (refs. 17 and
18) are presented in the right column.
1
+
states of the CS X Σ fragments formed in the CS 308-nm
2
two-photon photolysis with laser-induced fluorescence de-
tection, observed that CS was formed in its electronic
ground state with a bimodal vibrational distribution that
peaked at v′′ = 1 with a secondary maximum at v′′ = 5. In
In our excitation spectrum of rotationally excited CS, we
measured only high rotational levels, from N′ = 35 up to
N′ = 71. Because we observe these high rotational levels, the
1
+
1
+
centrifugal distortion constant D of the B Σ (v′ = 1) state
view of the fact that the CS X Σ fragments are predomi-
nantly formed in their v′′ = 1 vibrational state, and consider-
ing the significant predissociation of the v′ = 0 and v′ = 2
1
can be determined. The results of the rotational fit are shown
in Fig. 2a, and the difference plot between the experimental
and calculated line positions is presented in Fig. 2b. The im-
1
+
levels of the B Σ Rydberg state, it is not surprising that we
1
+
1
+
proved rotational constants for the CS B Σ (v′ = 1) state are
observe the CS X Σ fragments only in their v′′ = 1 vibra-
1 +
listed in Table 2 together with the CS X Σ ground-state
tional state. The O and S branches associated with the
1
+
1
+
constants of refs. 17 and 18.
B Σ (v′ = 1) ← X Σ (v′′ = 1) transition are not observed
because of the great difference in line strengths between the
Q and the O and S branches (16).
The two-photon dissociation of CS at about 308 nm pro-
2
duces, in addition to CS fragments, S atoms in various states
(
see dissociation pathways [1], [2], and [3]). Several transi-
The assignment of the peaks in the excitation spectrum of
Fig. 1 and the rotational analysis of the Q branch were per-
formed by assigning the measured rotational lines in an iter-
ative fashion. By using the published ground-state rotational
3
1
tions of the S ( P ) and S ( S ) fragments are observed fol-
J
0
lowing (2+1) ionization. These well-known absorption lines
are used for wavelength and kinetic-energy calibration. Dis-
1
1
+
sociation resulting in S ( D ) (route [2]) is not observed be-
constants (17), the B Σ excited-state rotational constants B′
were determined by fitting all the rotational energies of the
Q branch to the following expression:
2
cause no transitions can be excited via a (2+1) ionization
1
scheme with 308-nm photons. To observe S ( D ) atoms, the
2
photon energy must be shifted to higher energies.
′
′′
Photoelectron kinetic energy scans were obtained by one-
[
5]
Q(N′′) = v11 + (B – B )N′′(N′′ + 1)
1
1
1
+
photon ionization from the intermediate CS B Σ (v′ = 1; N′)
(D – D )N ′′ (N′′ + 1)
′′
′
2
2
2
+
+
–
1
1
state into the continua of the ionic ground state X Σ (v = 1;
©
2004 NRC Canada

Rijs et al.
747
Fig. 3. Photoelectron spectrum of rotationally hot CS, produced
Fig. 4. (1+1) REMPI excitation spectrum with electron detection
3
+
3
in the two-photon dissociation of CS . The spectrum is obtained
of the Σ ← a Π transition of CS photofragments in the one-
–1
2
by (2+1) ionization, by employing the Q(55) transition via the
photon energy range 33 075 – 33 400 cm (vacuum energies).
1
+
v′ = 1 level of the intermediate B Σ Rydberg state. (a) In the
2
+
+
spectrum, transitions to X Σ (v = 1, 2, 3) are shown; (b) more
+
detailed scan for ∆v = 0 (v = 1), showing some rotational struc-
ture.
observed (see Fig. 3b). Besides the Q(55) (∆N = 0) feature,
peaks are also observed at about 20–25 meV from the Q(55)
peak. These peaks can be assigned to ∆N = ±2 transitions.
The rotational spacings between the ∆N = 0 peak and the
+
+
∆
N = +2 and –2 peaks are expected to be B (4N + 6)
+
+
(
24 meV) and B (4N – 2) (23 meV), respectively. Here
B = 0.857662 cm (5) is the ionic rotational constant, and
N is the rotational quantum number of CS . Higher order
rotational contributions are neglected in this estimate. The
rotational structure in the photoelectron spectra of CS is sub-
ject to selection rules. For one-photon ionization from the
+
–1
+
+
1
+
B Σ (v′) state, the selection rule ∆N + ᐉ = odd applies,
where ∆N = N – N′ and ᐉ is a partial wave component of
+
the photoelectron (19, 20). In the present case, the CS
Rydberg electron occupies a 3sσ molecular orbital. In an
atomic-like picture, ionization of this 3sσ Rydberg electron
is expected to lead to p (ᐉ = 1) partial waves, and, on this ba-
sis, strong ∆N = even transitions would be expected; ∆N =
±
1 transitions are forbidden on the basis of these selection
rules. However, with the present quality of the rotationally
resolved photoelectron spectra, no firm conclusions can be
drawn.
Following two-photon dissociation of CS at 308 nm, the
2
CS photofragments can be formed in the triplet state, result-
3
3
ing in CS (a Π) + S ( P ). Figure 4 shows the one-photon ex-
J
–
1
citation spectrum in the energy range 33 075 – 33 500 cm ,
+
3
N ). Figure 3a presents the photoelectron spectra associated
corresponding to the CS fragment produced in its a Π state.
The features observed belong to the Σ (v′ = 0) ← a Π (v′′ =
2) transition (21, 22). The origin (v ) of this transition lies
with the Q(55) rotational transition at 65 077.6 cm– via v′ =
1
3
+
3
1
0
. The dominant peak at about 0.74 eV arises from the ∆v =
0
0
transition. The smaller peaks can be assigned to the ∆v =
at 282 nm, whereas we excite with ~300 nm. Ono and
Hardwick (21) observed three absorption bands at 282, 291,
+
(
v – v′) = +1, +2 transitions. The vibrational ∆v = 0 propen-
2
+
1
+
3 +
sity observed for this X Σ ← B Σ step is expected for one-
photon ionization of a Rydberg state.
and 300 nm. These bands are assigned to the Σ (v′ = 0) ←
3
a Π (v′′ = 0, 1, 2) transitions, respectively. In our experi-
3
+
3
Despite the high rotational excitation of the CS fragment,
the ionic spacings are not large enough to measure good-
quality rotationally resolved photoelectron spectra. However,
if we make a more detailed scan for the ∆v = 0 transition at
about 0.74 eV, some partially resolved rotational structure is
ment, we have studied only the Σ (v′ = 0) ← a Π (v′′ = 2)
transition. Since the same photons are used for the photo-
dissociation of CS and for the spectroscopy of CS, the other
2
transitions could not easily be accessed in a one-color exper-
iment. Our rotational assignment is based on the results of
©
2004 NRC Canada

7
48
Can. J. Chem. Vol. 82, 2004
3
Fig. 5. Photoelectron spectrum of CS (a Π), resulting from the
and nearly all them are formed in their ground vibrational
3
+
(
1+1) photoionization via the Σ Rydberg state.
states (2, 3). The photodissociation of CS produces both
2
ground-state and excited-state CS fragments and results in
vibrationally excited CS species, both in the singlet elec-
1
+
tronic X Σ ground state and in the electronically excited
3
triplet a Π state. In the photodissociation process of OCS
and N O, the C—O and the N—N fragments appear to act
2
solely as spectators, while in CS the nonbonding electrons
2
of both S atoms contribute to the absorption and both C—S
bonds are excited and stretched (24). Ultimately, if one C—S
bond breaks, the other is strongly vibrationally excited.
The photoelectron spectra of ground-state CS photo-
fragments are dominated by ∆v = 0 propensity, as was the
case with the photoelectron spectra of ground-state N and
2
CO. However, the photoelectron spectra of N and CO could
2
be measured with excellent rotational resolution, whereas in
the case of CS it appears more difficult to obtain rotationally
resolved photoelectron spectra. This is mostly because the
+
rotational constant of the CS ion is approximately half that
of N2+ or CO .
+
Finally, the fact that our experiments on CS, both in its
singlet and triplet electronic states, have been performed in
the ~1 T field of a magnetic bottle spectrometer should not
affect the observed dynamics. Systematic studies have
shown that possible magnetic field effects in this type of
spectrometer may only be significant for high Rydberg states
close to the ionization threshold (25–27).
Ono and Hardwick (21). The complexity of the rotational
structure that is evident from Fig. 4 is typical for a Σ ← Π
transition between the two states described in Hund’s case
3
+
3
(
b) (23). Because of the high threshold energy of 7.88 eV for
3
the formation of CS (a Π) (see Table 1) and the vibrational
excitation (v′′= 2), less energy is available for excitation of
the internal degrees of freedom, resulting in rotationally cold
Conclusions
3
(
N′′= 4–22) CS (a Π) (21). This situation is in sharp contrast
1
+
The photodissociation dynamics of CS2 at about 308 nm
encompasses a singlet and a triplet CS dissociation channel.
The photodissociation via the singlet channel produces
to the formation of CS (X Σ ) with significant rotational ex-
1
+
citation. Since CS (X Σ ) is produced in a (2+1) and CS
3
(
a Π) in a (1+1) REMPI experiment, the very different con-
1
+
rotationally hot CS (X Σ ) fragments in their first
vibrationally excited level. A rotational distribution of CS
extending from N′ = 35 up to N′ = 71 (with a maximum at
N′ = 58) has been observed and assigned. For the first time,
a (2+1) high-resolution partly rotationally resolved excita-
ditions do not allow any reliable conclusions about branch-
ing ratios between both channels.
Figure 5 presents the experimental photoelectron spectrum
3
obtained for (1+1) photoionization of CS (a Π, v′′ = 2) via
3
+
–1
the CS ( Σ , v′ = 0) Rydberg state at 33 327.8 cm , produc-
1
+
1 +
2
+
+
+
tion spectrum of CS (X Σ ) via the Rydberg level B Σ has
ing the X Σ (v ) ionic ground state of CS . The dominant
peak in the photoelectron spectrum at about 0.60 eV is the
been recorded. Improved spectroscopic rotational parameters
have been obtained for the CS (B Σ ) state. The other disso-
ciation channel of CS at 308 nm results in the production
1
+
∆
v = 0 transition. The neighboring peaks at the left-hand
2
side of the spectrum arise from ∆v = +1, +2 transitions. No
3
of CS (a Π) in its v′′ = 2 vibrational level, with low rota-
rotationally resolved features are observed in the photoelec-
3
tional excitation. In both cases the photoelectron spectra
were dominated by ∆v = 0 propensity, with much weaker
transitions involving ∆v = 1 and 2.
tron spectrum of CS (a Π, v′′ = 2) because of the low rota-
+
tional excitation and the small rotational B constant. The
shoulder on the right-hand side of the ∆v = 0 peak is the re-
1
sult of nonresonant multiphoton ionization of S sulfur at-
Acknowledgements
oms.
In summary, the photodissociation of CS produces CS
2
AMR acknowledges the Holland Research School of Mo-
lecular Chemistry for a Ph.D. fellowship. CAdL acknowl-
edges very useful discussions with Professor J.M. Dyke and
members of his group during a stay in Southampton in the
context of the EC Network on Reactive Intermediates.
molecules both in the singlet ground state and in a triplet ex-
1
+
cited state. The ground state (X Σ , v′′ = 1) formed is highly
3
rotationally excited, while the triplet state (a Π, v′′ = 2) gen-
erated is rotationally cold. Comparing the results of the
photodissociation of CS with previous studies of the photo-
2
dissociation of the similar molecules N O (2) and OCS (3),
the photodissociation of these molecules produced rotation-
2
References
ally hot N and CO photofragments and O and S atoms in
2
1. A.M. Rijs, E.H.G. Backus, C.A. de Lange, N.P.C. Westwood,
and M.H.M. Janssen. J. Electron Spectrosc. Relat. Phenom.
112, 151 (2000).
1
their D singlet excited states. In the photodissociation of
2
CS we observe both similarities and differences. In the case
2
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