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Rotational Analysis for the Doppler-Free Photoelectron Spectrum of Water Using the Spectator Model† Mark S. Forda and Klaus Mu¨ller-Dethlefs* The Photon Science Institute and School of Chemistry, The UniVersity of Manchester, Alan Turing Building, Oxford Road, Manchester M13 9PL, U.K.
M. Kitajima and H. Tanaka Department of Physics, Sophia UniVersity, Chiyoda-ku, Tokyo 102-8554, Japan
Y. Tamenori and A. De Fanis SPring-8/JASRI, Sayo-gun, Hyogo 679-5198, Japan
Kyoshi Ueda* Institute of Multidisciplinary Research for AdVanced Materials, Tohoku UniVersity, Sendai 980-8577, Japan ReceiVed: March 19, 2010; ReVised Manuscript ReceiVed: August 30, 2010
A photoelectron spectrum of H2O has been recorded at a resolution of 2 meV under Doppler-free conditions. ˜ + 2B1 and A ˜ + 2A2 Complex rotational structures appear in the individual vibrational states of the electronic X states in H2O+. The rotational structures are analyzed and well reproduced using a spectator orbital model developed for rotationally resolved photoelectron spectroscopy. Introduction ˜ + 2B1 The spectroscopic study of the water cation in the X +2 ˜ and the A A1 states has provoked a great deal of interest using a plethora of techniques. The system has been recently been studied using IR adsorption and emission by Chen et al.,1,2 Vervloet et al.,3 Oka et al.,4 Stickland et al.,5 and by Lew and Heiber.6 Both Saykally et al.7 and Brown et al.8 have used laser magnetic resonance for the ground state. Water is given as one of the first examples of spin rotation coupling in photoelectron spectroscopy in the ZEKE study by Merkt et al.9 Rydberg states converging to these levels have been investigated in a study by Glab et al.10 Earlier spectroscopic studies were carried out using photoelectron spectroscopy;11-14 in these studies only vibronic structure was observed (although some rotational structure was ˜ + state in ref 14, this was ascribed to the spectra of the A analyzed in an empirical manner). Jet cooled photoionization ˜ + and B˜+ states using spectra have been recorded for both the A 15-17 single and multiphoton schemes; analyses of these high resolution spectra have been carried out, employing an ab initio approach18 and employing multichannel quantum defect theory to understand electronic-rotational channel interactions in Rydberg spectra that approach the ionization limit.19,20 ˜ + state has attracted much interest as the water cation The A adopts a quasilinear geometry, and as such is Renner-Teller ˜ + and A ˜ + states of the water cation arise from the active. The X two components of the 2Πu linear structure which are split by the Renner Teller effect. The ground state exhibits a deep ˜ + state is quasilinear; hence a substantial minimum, but the A †
Part of the “Klaus Mu¨ller-Dethlefs Festschrift”. * Corresponding authors. E-mail:
[email protected],
[email protected]. a Now at: Chemistry Research Lab, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA, U.K.
body of theoretical work exists to account for the rovibronic energy levels.21-24 The rotational structure in high resolution photoionization spectroscopy is a probe of the ionization dynamics.25-31 It has been demonstrated that the ZEKE spectra of molecules with relatively small rotational constants, i.e., benzene, fluorobenzene, butylbenzene, and V3, can be reproduced using a simple model that does not explicitly take into account final state interactions.32 The final state interactions are not a problem when it is applied to conventional photoelectron spectra, as ionization takes place directly into the continuum; hence, in this paper, it is shown that the model of the ionization dynamics also works reasonably well for conventional photoelectron spectroscopy. To observe the rotationally resolved photoelectron spectra, one needs a resolution of at least 3 meV. The Doppler broadening due to thermal motion of the molecule at room temperature, on the other hand, amounts to 7 meV for the X2B1 band excited by the He I radiation. Thus, it is indispensable to eliminate the Doppler broadening. The Doppler energy shift is given by the scalar product of the electron momentum and the momentum of the emitter. Thus, if one uses a well-collimated molecular beam, whose velocity component perpendicular to the beam direction is negligible, as a target and observes the electron emission in the direction perpendicular to the molecular beam, then one can suppress the Doppler broadening. The Doppler-free rotationally resolved photoelectron spectrum of the ¨ hrwall and Baltzer.33 ˜ + 2B1 (0,0,0) band was first observed by O X In the present experiment, we extend the observation to fully ˜ + 2B1 and cover all the vibrational substates observed in the X ˜ + 2A1 states. the A The analysis of the photoelectron spectra yield a series of parameters that relate to the orbital from which ionization occurs and can be regarded as a reasonably sensitive probe of the symmetries involved in the transition.28,29,34-37 The dependence
10.1021/jp102496n 2010 American Chemical Society Published on Web 09/29/2010
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TABLE 1: Correlation between the Basis Functions, |l′λ′〉 ( |l′ - λ′〉, and the C2W Symmetry of Watera projection axis a b c a
even l′ A1 +
E E+ E+
A2(b) +
O EO-
B1(c) -
O O+ E-
odd l′ B2(a) -
E OO+
A1(b) -
O E+ O+
A2 -
E EE-
B1(a) +
E O+ O-
B2(c) O+ OE+
E (O) corresponds to even (odd) values of λ′.
of the ionization dynamics on the symmetries is such that the symmetry of the orbital from which ionization occurs is given by the product of the initial and final state symmetries (1). The symmetry can then be used to resolve which angular momentum contributions describe the orbital by way of the coefficients, γ′l′λ′(.29 These are denoted in terms of symmetry adapted basis functions, |l′λ′〉 ( |l′ - λ′〉, having angular momentum, l′, and its projection, λ′. The value of l′ will correlate with the maximum value of ∆N () N+ - N′′), and the value and symmetry of λ′ will correlate with changes in its projection. Using the correlation tables given in ref 29, it is possible to construct a correlation table (Table 1) for the water molecule to determine which values of l′ and λ′ are appropriate, given the axis chosen for the projection of the angular momentum.
Γelec ⊆ ΓInitial X ΓFinal
(1)
As the process of ionization cannot be described within the Born-Oppenheimer approximation, in practice, the change in vibrational motion is also important; hence the symmetries involved are strictly vibronic as opposed to purely electronic. In the photoelectron spectrum of water it is possible to examine the effects of the vibrations on the ionization dynamics: In the ˜ + state of the cation there is excitation of both the symmetric X ˜ + state there is a and asymmetric stretches, and in the A progression in the Renner active bending vibration. Experimental Section The spectrometer used in the experiment was a 200 mm radius hemispherical electron spectrometer (Gammadata-Scienta SES2002).38 He I radiation was generated with an electron cyclotron resonance (ECR) UV lamp (Gammadata-Scienta, VUV 5000) giving very intense light with a measured line width of less than 1.2 meV. The light from the radiation source was introduced into the ionization region by a quartz capillary without further monochromatization. Water vapor was introduced into the ionization region via Doppler free beam device (MB Scientific, JD-01).39 The device consists of an orifice of 1 mm × 8 mm, covered by a 1 mm thick multicapillary array that has the open area ratio of approximately 70%. The diameter of each capillary is 10 µm. The surface facing the excitation region is covered with a conductive layer of graphite with a suitable work function. An electrode structure surrounds the orifice, which allows precision modeling of the electrostatic potential in the target volume. The electrode voltages, as well as the voltage applied to the device body, can be externally adjusted to compensate for plasma potential gradients and work-function drifts in the ionizing region. The multicapillary array permits a much higher target pressure than a single tube device. The inlet pressure of an effusive beam source is limited roughly to 1 Torr, i.e., the level where the
˜ + 2B1 state of the water Figure 1. Photoelectron spectrum of the X cation.
mean free path for intermolecular collisions matches the channel length. The achievable target pressure scales as the square root of the number of channels when all other parameters are kept constant. The channel length to diameter ratio (i.e., 100 in our beam device) determines the beam divergence angle. The Doppler width is proportional to the width of the velocity distribution of the atoms or molecules parallel to the electron emission direction. A reduction of the Doppler width scales linearly with the ratio between the effective exciting beam diameter (typically 1 mm) and the distance to the beam (typically 5 mm). A reduction of more than 1 order of magnitude can be easily achieved with minimal intensity loss. The molecular beam is fed perpendicular to both the ionizing radiation and the acceptance angle of the spectrometer. The entrance slit of the spectrometer is parallel to the target volume. In this alignment, the Doppler effect can be suppressed, because the transverse velocity component of the molecular beam is negligible. Results and Discussion ˜ + State. Figure 1 shows the photoelectron spectrum of water X ˜ + state corrected to the ion internal energy. Previous in the X work has clearly assigned the bands as indicated in the ˜ + state occurs from the b1 spectrum.4-6 Ionization into the X orbital; this can be described as a “p” orbital localized on the oxygen atom, which is polarized along the c axis of the water molecule. However, the b-axis is chosen for the molecule fixed z-axis, as this is the axis about which water exhibits rotational symmetry. Given that the ionizing transition is between states with A1 and B1 symmetries the spectator orbital has b1 symmetry. Referring to table 1, suggests that the coefficients, γ′l′λ′(, will correspond to the following values of l′λ′(: 11-, 21+, 31-, 33-, etc. As is discussed in ref 37, photoionizing transitions have often been described in terms of a-, b-, and c-type transitions. For bound-bound transitions changes in the Ka and Kc labels, which respectively correspond to the prolate and oblate limiting values of the K quantum number, are identified with these types of transition. For odd l′, changes in Ka will be odd and changes in Kc will be even, giving rise to what are traditionally called c-type transitions, whereas for even l′, changes in Ka will be even and Kc will be odd, giving rise to what are traditionally called a-type transitions. As previously discussed, the identification of the transitions with traditional a-, b-, and c-type transitions is inappropriate, particularly as they have nothing to do with the orientation of the transition dipole moment. Figure 2 gives a deconvolution of the origin band into the four allowed contributions - the simulations are based on
Doppler-Free Photoelectron Spectrum of Water
J. Phys. Chem. A, Vol. 114, No. 42, 2010 11135 TABLE 2: Spectator Orbital Coefficients for Ionisation into ˜ + State of the Water Three Vibrational Levels of the X a Cation γ′ (
(000)
(010)
(100)
-
-0.32 0.75
-0.28 0.80 0.28 0.46
-0.27 0.78
l′λ′
11 213133a
0.58
0.56
-
The contribution from 31 is completely vibronic in nature.
˜ + state origin band (top) into the Figure 2. Deconvolution of the X four components with l′ < 4, which are needed to simulate the band.
˜ + state of the water cation. Figure 4. Photoelectron spectrum of the A The spectrum exhibits a long progression in the Renner-Teller active bending vibration, which is seen in the alternating band profiles, arising from even and odd K states. The two very sharp lines between 25 000 and 30 000 cm-1 are the Ar PES lines.
˜ + 2B2 state of the Figure 3. Fits to the three major bands seen in the X water cation. The “spectator” orbital parameters used to describe the (000) and (001) bands are nearly identical, whereas the (010) band shows a distinct difference; this is attributed to vibronic effects perturbing the spectator orbital.
rotational constants for the neutral and ionic ground states of ˜ state, and ref water published previously (from ref 40 for the X ˜ + state). It is clear from the width of the origin band 6 for the X that there are no significant contributions from l′ > 3. If the orbital were purely atomic and centered on the center of mass of the water molecule, the description as a “p” orbital would indicate that only the 11- contribution would be necessary to describe the ionization dynamicssthis deconvolution highlights the inadequacy of such a description. The symmetry allowed contributions to the spectator orbital are combined to give the simulations in Figure 3. Figure 3 also shows this analysis extended to the bands arising from the symmetric stretching vibration, (100), and the bending vibration, (010). Table 2 summarizes the values obtained for the spectator orbitals coefficients. The origin band and the symmetric stretch, within the uncertainty of the fit yield the same values for the parameters. A previous analysis of this transition, focusing on the partial wave matrix elements that describe the outgoing electron,18 similarly identified that the strongest peaks do not arise as the c-type transitions, consistent with ionization from an atomic “p”
˜ + state νb ) 10 (K ) 1, 3) and νb ) Figure 5. Deconvolution of the A 9 (K ) 0, 2) vibrations.
orbital; instead, the so-called a-type transitions (they are in this case not the same as conventional a-type transitions, which would have to arise from an l′ ) 1 component) are stronger, arising via the l′ ) 2 component. The description was given
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TABLE 3: Spectator Orbital Coefficients for the Major Components (K ) 0, 1) of the νb ) 6 to νb ) 13 Levels γ′(K,νb) l′λ′(
Π, 6
-
11 20+ 22+ 313340+ 42+ 44+
Σ, 7 0.40 0.66
0.81
Π, 8
Σ, 9
Π, 10
Σ, 11
0.67 0.68
0.36 0.70 -0.21
-0.26 0.72 0.34 0.38
0.53 0.69
0.42 0.24 0.32
0.33
0.36
0.21
0.34
0.22 0.54
0.30 0.40 0.38
0.28
Π, 12
Σ, 13
0.79 0.33
0.45 0.26 0.34
0.43 0.28
0.66 0.22 0.36
TABLE 4: Spectator Orbital Coefficients for the Minor Components (K ) 2, 3) of the νb ) 6 to νb ) 13 Levels γ′(K, νb) l′λ′( Φ, 6 -
11 20+ 22+ 313340+ 42+ 44+ rel I
∆, 7
Φ, 8
0.62 0.56 0.56
0.32 0.64
Φ, 10 -0.35
0.28 -0.30 0.85
∆, 9
0.78
∆, 11
Φ, 12
∆, 13
-0.51
0.53 0.27 0.93 -0.47 0.60 0.40 -0.37 0.36 -0.26 -0.44 -0.80 -0.92 0.31 -0.71 0.21 0.82 0.20 0.30 0.31
that the a-type transitions are molecular in nature and the c-type transitions are atomic-like; however, examining the parameters given here suggests a more detailed story. Indeed, the a-type transitions arising from the 11- component will mostly correspond to the atomic-like nature of the b1 orbital. However, the dominant 21+ component mostly arises as a consequence of the dynamical information that is implicitly included in the spectator orbital. The presence of the 33+ component, which gives rise to nontypical c-type transitions, will have its origins both in the dynamics of the ionization process and from the perturbation from an atomic like “p” orbital. The bending vibration, which logically couples more strongly with the rotation, shows a significant deviation, notably from
the appearance of a contribution from the 31- partial wave function. Because the electronic structure is the same in all three cases, this is an indication of the effect of vibronic coupling. The fit to the bending vibration (Figure 3) does suggest that even higher angular momentum terms that have not been included are still necessary, indicating that the vibronically active vibration is able to mediate an angular momentum transfer from the core rotation to the outgoing electron larger than is possible in the purely electronic transition. ˜ + state of the water cation yields the ˜ + State. The A A photoelectron spectrum given in Figure 4, again corrected to the internal energy of the ion. The photoelectron spectrum shows a progression in the bending vibration, which, as this is a quasilinear molecule is characterized by two quantum numbers, νb and K. These are usually combined into the single vibrational quantum number ν2 ) 2νb + K + (Λ ) 1), as this quantum number is representative of the energy of the vibration; thus it is seen that the bands seen in Figure 4 arise from odd and even values of K, giving rise to the alternating band profiles, this has previously been analyzed empirically in a PES study.14 ˜ + state, the To analyze the rotational spectroscopy of the A a-axis must be chosen as the molecular z-axis, as this corresponds to the limiting linear structure of the molecule. Thus the allowed contributions of l′λ′( from Table 1 are 11-, 20, 22+, 31-, 33-, etc. (00 does not give rise to any intensity). In this case the 11- component (as with all odd l′ components) gives rise to “b-type” transitions, but the 20 (as with all even l′ components) clearly gives rise to transitions that cannot be described as a-, b-, or c-type, arising from coupling to a spectator ˜+ orbital that is totally symmetric in the D2 group. For the A state, it is likely that higher values of l′ are necessary, as the spectator orbital is not particularly atomic like. The spectator orbital coefficients, which arise from the projection of the final state vibronic wave function onto that of the initial state will depend on the vibronic state; hence a different set of coefficients must arise from each value of K, and for K > 0, from each of the parities. The spectra of the Σ/∆(0,10,0) and the Π/Φ(0,11,0) levels are deconvoluted using molecular parameters from refs 22, 1,
˜+ r X ˜ transition that have been analyzed. Figure 6. Fits to the eight bands of the A
Doppler-Free Photoelectron Spectrum of Water and 2 (the vibrational assignments have been shown to be incorrect in the earlier publication); no attempt to improve on these has been made because we are working at lower resolution, yielding the spectra given in Figure 5. The figures are only shown for l′ < 4 although we carried out the analysis to l′ ) 6. It was seen that l′ > 4 did not contribute significantly to the bands. The values of the parameters used to fit to the experimental spectra are listed in Tables 3 and 4. The parameters are all normalized, such that the sum of squares for a given K sub-band is 1. For the ∆ sub-bands the intensity relative to the Σ sub-band is given, and for the Φ sub-band the intensity relative to the Π sub-band is given. The fits to the eight bands of the ˜ transition are in Figure 6. ˜+ r X A By comparison with the parameters needed for the ground state of the cation, it is apparent that the spectator orbital is much less atomic in nature. This is to be expected for a number of reasons: First, the “p” orbital lies in the plane of the molecule, and as such is perturbed by the hydrogen atoms to a much greater extent. Also there is a great deal more excitation in the bending vibration, which, as was seen in the ground state, has a significant impact on the spectator orbital. Finally, the large structural change in going from a bent to a linear molecule will mean that the spectator orbital will not truly resemble the “p” orbital that is predicted, in the absence of a structural change. Unfortunately, it is not easy to separate these effects. The origin band does not have significant intensity, and so it is not possible to eliminate vibronic effects, and as vibronic effects are minimized, clearly the effect of the geometry change becomes more significant. Qualitatively it is seen that similar trends are seen for the same value of K. The K ) 0 levels, which should most closely resemble the spectrum from a purely electronic spectator orbital tend to have strong contributions form 11- and predominantly 20+. Alone these contributions could describe a “p” orbital shifted along the axis from the center of mass; however, significant contributions are also seen from l′ ) 4. The most striking feature of the K ) 1 levels is that the (060) level shows a profile very different from the others. It is conceivable that there is some resonance here, in which case it would be very hard to infer anything meaningful from this. The remaining three spectator orbitals no longer exhibit a strong contribution corresponding to the pΠ orbital, this is consistent with the fact that the Π component is projected out of the spectator orbital. It is hard to justify the values for the K ) 2 and K ) 3 levels, as the complexities of the vibronic coupling become intractable. As these levels are partially obscured by the lower K bands, there is considerable uncertainty in the values of the parameters. With the higher K levels it appears that there is a tendency to higher values of l′; as the intensity of these transitions is split between more transitions, they make a weaker contribution to the spectrum. Conclusions The photoelectron spectrum of water recorded at high resolution has provided an opportunity to study the effect of ˜ + state it is seen vibrations on the ionization dynamics. In the X that while the stretching vibration has a negligible effect, the effect of the bending vibration, which couples more effectively ˜ + state, which is quasiwith the rotation, is significant. In the A linear and subject to the Renner effect, there is a long progression in the bending vibration. Both the extent of the vibration and its projection on the molecular axis, K, were seen to affect the spectator orbital. Increases in K appeared to lead to an increase in the high l′ contributions, probably as the lower
J. Phys. Chem. A, Vol. 114, No. 42, 2010 11137 l′ contributions are projected out of the spectator orbital, particularly those contributions with λ′ ) K. The effect of going from a bent molecule to a linear molecule is reduced with the degree of vibrational excitation. These will have a competing effect; thus changes in the spectator orbital did not follow any simple trends. Acknowledgment. The work was partly supported by Grantsin-Aid for Scientific Research from Japan Society for Promotion of Science. We acknowledge Y. Takata of JASRI/SPring-8 and P. Baltzer and M. Matsuki of MBS for assistance in installation of the apparatus and performing test. References and Notes (1) Gan, Y.; Yang, X.; Guo, Y.; Wu, S.; Li, W.; Liu, Y.; Chen, Y. Mol. Phys. 2004, 102, 611. (2) Wu, S.; Yang, X.; Guo, Y.; Zhuang, H.; Liu, Y.; Chen, Y. J. Mol. Spectrosc. 2003, 219, 258. (3) Huet, T. R.; Bachir, I. H.; Destombes, J.-L.; Vervloet, M. J. Chem. Phys. 1997, 107, 5645. (4) Huet, T. R.; Pursell, C. J.; Ho, W. C.; Dinelli, B. M.; Oka, T. J. Chem. Phys. 1992, 97, 5977. (5) Brown, P. R.; Davies, P. B.; Stickland, R. J. J. Chem. Phys. 1989, 91, 3384. (6) Lew, H.; Heiber, I. J. Chem. Phys. 1973, 58, 1246. (7) Strahan, S. E.; Mueller, R. P.; Saykally, R. J. J. Chem. Phys. 1986, 85, 1252. (8) Mu¨rtz, P.; Zink, L. R.; Evenson, K. M.; Brown, J. M. J. Chem. Phys. 1998, 109, 744. (9) Merkt, F.; Signorell, R.; Palm, H.; Osterwalder, A.; Sommavilla, M. Mol. Phys. 1998, 95, 1045. (10) Glab, W. L.; Child, M. S.; Pratt, S. T. J. Chem. Phys. 2004, 120, 8555. (11) Brundle, C. R.; Turner, D. W. Proc. R. Soc. London, Ser. A 1968, 307, 27. (12) Potts, A. W.; Price, W. C. Proc. R. Soc. London, Ser. A 1972, 307, 181. (13) Karlsson, L.; Mattsson, L.; Jadrny, R.; Albridge, R. G.; Pinchas, S.; Bergmarck, T.; Siegbahn, K. J. Chem. Phys. 1975, 62, 4745. (14) Dixon, R. N.; Duxbury, G.; Rabalais, J. W.; Åsbrink, L. Mol. Phys. 1976, 31, 423. (15) Page, R. H.; Larkin, R. J.; Shen, Y. R.; Lee, Y. T. J. Chem. Phys. 1988, 88, 2249. (16) Tonkyn, R. G.; Wiedmann, R.; Grant, E. R.; White, M. G. J. Chem. Phys. 1991, 95, 7033. (17) Glab, W. L.; Child, M. S.; Pratt, S. T. J. Chem. Phys. 1998, 109, 3062. (18) Wang, K.; Lee, M.-T.; McKoy, V.; Wiedmann, R. T.; White, M. G. Chem. Phys. Lett. 1994, 219, 397. (19) Child, M. S.; Jungen, Ch. J. Chem. Phys. 1990, 93, 7756. (20) Gilbert, R. D.; Child, M. S.; Johns, J. W. C. Mol. Phys. 1991, 74, 473. (21) Jungen, Ch.; Merer, A. J. Mol. Phys. 1980, 40, 1. (22) Jungen, Ch.; Hallin, K.-E. J.; Merer, A. J. Mol. Phys. 1980, 40, 25. (23) Jungen, Ch.; Hallin, K.-E. J.; Merer, A. J. Mol. Phys. 1980, 40, 65. (24) Brommer, M.; Weis, B.; Follmeg, B.; Rosmus, P.; Carter, S.; Handy, N.; Werner, H.-J.; Knowles, P. J. J. Chem. Phys. 1993, 98, 5222. (25) Ford, M. S.; Lindner, R.; Mu¨ller-Dethlefs, K. Mol. Phys. 2003, 101, 705. (26) Ford, M. S.; Mu¨ller-Dethlefs, K. Phys. Chem. Chem. Phys. 2004, 6, 23. (27) Ford, M. S.; Tong, X.; Dessent, C. E. H.; Mu¨ller-Dethlefs, K. J. Chem. Phys. 2003, 119, 12915. (28) Ford, M. S.; Mackenzie, S. R. J. Chem. Phys. 2005, 123, 084308. (29) Ford, M. S.; Mu¨ller-Dethlefs, K. Submitted for publication to J. Chem. Phys. (30) Wang, K.; McKoy, V. Annu. ReV. Phys. Chem. 1995, 46, 275. (31) Willitsch, S.; Hollenstein, U.; Merkt, F. J. Chem. Phys. 2004, 120, 1761. (32) Merkt, F.; Softley, T. Int. ReV. Phys. Chem. 1993, 12, 205. ¨ hrwall, G.; Baltzer, P. Chem. Phys. Lett. 1999, 308, 199. (33) O (34) Lindner, R.; Sekiya, H.; Mu¨ller-Dethlefs, K. Ang. Chem. Int. Ed. 1993, 32, 1364. (35) Habenicht, W.; Reiser, G.; Mu¨ller-Dethlefs, K. J. Chem. Phys. 1991, 95, 1809. (36) Wo¨rner, H. J.; Merkt, F. Angew. Chem. Int. Ed. 2006, 45, 293. (37) Signorell, R.; Merkt, F. Mol. Phys. 1997, 92, 793.
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(38) Shimizu, Y.; Ohashi, H.; Tamenori, Y.; Muramatsu, Y.; Yoshida, H.; Okada, K.; Saito, N.; Tanaka, H.; Koyano, I.; Shin, S.; Ueda, K. J. Electron Spectrosc. Relat. Phenom. 2001, 114-116, 63. (39) Tamenori, Y.; Kitajima, M.; De Fanis, A.; Shindo, H.; Furuta, T.; Machida, M.; Nagoshi, M.; Ikejiri, K.; Yoshida, H.; Ohashi, H.; Koyano, I.; Tanaka H. Baltzer, P.; Ueda, K. In Proceedings of the
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