Raman Chirped Adiabatic Passage Probed by X-ray Spectroscopy

We report a theoretical study of the selective vibrational excitation of a HCl molecule achieved by Raman chirped adiabatic passage (RCAP) and probed ...
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Raman Chirped Adiabatic Passage Probed by X‑ray Spectroscopy Selma Engin, Nicolas Sisourat,* Patricia Selles, Richard Taïeb, and Stéphane Carniato Laboratoire de Chimie Physique Matière et Rayonnement, Université Pierre et Marie Curie - CNRS (UMR 7614), Paris, France ABSTRACT: We report a theoretical study of the selective vibrational excitation of a HCl molecule achieved by Raman chirped adiabatic passage (RCAP) and probed by X-ray photoelectron spectroscopy (XPS). It is demonstrated that HCl can be prepared in any vibrational level up to ν = 9 with nearly complete population inversion. We explore the effects of both the rotation of the molecule and of the temperature on the RCAP process, which is proved to be very robust. Furthermore, we emphasize that XPS spectra at the chlorine K-shell threshold show characteristic signatures of the populated vibrational level, allowing us to follow the RCAP process.

I. INTRODUCTION Spectroscopic studies of molecules are generally limited to the Franck−Condon region, and thus only a small portion of the potential energy surfaces (PESs) can be probed. Information beyond this region can be obtained by preparing the molecules in some intermediate state that has a larger interatomic distribution, by, for example, laser pumping1 or core excitation.2 In the former case, the laser pump prepares a coherent superposition of vibrational eigenstates that is probed with a delayed pulse. In the latter case, one uses the nuclear dynamics on the core-excited PES to explore far from the Franck− Condon region. A better control can be achieved if the system is prepared in a well-defined excited vibrational eigenstate. In the case of core-excitation, this can be done by fine-tuning of the X-ray photon energies.3 In a pump−probe scheme, an intense specially designed laser pump field allows a selective vibrational excitation. Furthermore, such preparation of molecules in excited vibrational levels leads to a coherent control of chemical reactions.4 Selective vibrational excitation by laser pulses can be achieved by climbing the corresponding ladder by successive one-level transitions.5 Adiabatic passage techniques have been used successfully for climbing electronic, vibrational, and rotational ladders.6 Among these techniques, the Raman chirped adiabatic passage (RCAP)7 is a very promising scheme using two superimposed laser pulses (pump and Stokes). On the basis of Raman two-photon resonant transitions (see Figure 1), population inversion between two successive vibrational levels is achieved. Furthermore, one or both laser pulses are frequency chirped such that the frequency difference of the two laser pulses smoothly decreases in time, adjusting to the anharmonicity of the molecular potential and ensuring the adiabatic evolution of the system. Efficiency of RCAP has been theoretically demonstrated on H2, H2+,8,9 O2, and Cl210 and has been experimentally achieved on CO2 molecule.11 In a previous paper,12 we showed that RCAP technique is an efficient method to prepare fixed-in-space HCl molecules in a © 2013 American Chemical Society

Figure 1. Schematic view of the RCAP process. Two lasers (pump and Stokes) are used to climb the vibrational ladder by successive one-level transitions. One of the two laser pulses is frequency chirped such that the frequency difference of the two laser pulses smoothly decreases in time, adjusting to the anharmonicity of the molecular potential.

given ν vibrational level with nearly complete population inversion. It was also demonstrated that XPS is an appropriate tool to probe the quantum state of a molecule following the population transfer because of the so-called chemical shifts. In the present paper, we report on the RCAP process, taking into account the molecular rotation and the effects of the temperature to simulate present day experimental conditions. We show that efficient population transfer can still be achieved up to ν = 9 with rotating molecules because of optimized laser pulses parameters. Higher selectivity of the RCAP process is obtained at lower temperatures. We then demonstrate that the Special Issue: Stereodynamics Symposium Received: January 31, 2013 Revised: April 3, 2013 Published: April 3, 2013 8132

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for the time-dependent expansion coefficients, which was solved with the Adams−Bashforth−Moulton predictor− corrector integrator.14 To simulate the RCAP process in HCl, we considered the X1Σ+ GS and a collection of low-lying (2−4)1Σ+ and (1−6)1Π spin-singlet excited states in the energy range up to the first ionization potential (Ip = 12.75 eV15). For each state, the PES and the dipole transition moment were calculated using an augcc-pCVQZ and an aug-cc-pVQZ atomic Cartesian−Gaussian basis set16 centered on the Cl and H atoms, respectively, and the post Hartree−Fock configuration interaction method including up to quadruple electronic excitations (CI-SDTQ), as implemented in GAMESS(US) ab initio package.17 We had to perform the calculations in C1 symmetry group to obtain the transition dipole moments from Σ+ to Π states. Owing to the large numbers of configurations in such symmetry, we included only excited configurations up to triple excitations. The PESs of the ground and low-lying excited states of HCl are shown in Figure 2. They agree well with the previous results

vibrational state of the molecule during the RCAP process can be probed by XPS at the chlorine K-shell threshold. Effects of the temperature on the XPS spectra are finally discussed. Atomic units are used in the following, unless otherwise stated.

II. METHODS A. RCAP. The RCAP process (see Figure 1) was simulated by solving the time-dependent Schroedinger equation in the adiabatic elimination approximation.13 Within this model, the nuclear dynamics in the excited electronic states can be eliminated because they are weakly populated. We thus only need to consider the nuclear wave function in the electronic ground state (GS). The interactions with the electronic excited states are implicitly included in an effective coupling operator. The total Hamiltonian is then given by J2 1 ∂2 1 + V0(R ) + − αΣ(R ),2(t ) cos2 θ 2 2 2μ ∂R 2 2μR 1 − αΠ(R ),2(t ) sin 2 θ (1) 2

H=−

where V0 is the potential energy curve of the HCl electronic GS, J2 is the squared angular momentum operator, and θ is the angle between the molecular axis and the laser electric field. The effective coupling operators α∑(R) and αΠ(R) are given by αΣ(Π)(R ) =

∑ i ∈Σ(Π)

|di0(R )|2 (Vi (R ) − V0(R ))

(2)

where di0(R) is the dipole transition moment between the electronic GS and excited state i and Vi(R) is the potential energy curve of the excited state. The two laser fields are chosen to be linearly polarized and parallel. The electric field ,⃗ (t) is thus defined as ,⃗ (t ) = ,⃗oU (t )[sin(ωit − (cr /2)t 2) + sin(ωst )]

Figure 2. Ab initio PES of the first low-lying states of HCl used in this study. The solid lines represent the Σ states while the dashed lines are used for the Π states. These PESs were used to compute the effective coupling operators (eq 2).

(3)

The parameters ωs, ωi, and cr are the Stokes pulsation, the initial pump pulsation, and the chirp rate, respectively. The carrier envelope U(t) is trapezoidal. The adiabatic elimination approximation is valid as long as the excited electronic states are far above the electronic GS compared with the photon energy because this approximation breaks down when the excited states are strongly populated. Note that the RCAP technique is efficient only when the excited states are also weakly populated and control is otherwise lost. We have evaluated that for HCl the adiabatic elimination approximation is valid and the RCAP is efficient up to ν = 9. Above this vibrational level, the first excited state is close in energy to the GS and starts to be significantly populated. Therefore, we simulated the RCAP process only up to this level. For each initial rotational state (J0, M0), the time-dependent 2-D nuclear wave function is written as Ψ J0 , M0(R , θ , t ) =

of Bettendorff et al.18 The PES of the electronic GS has a minimum located at around R = 1.27 Å, which is ∼4.46 eV below the dissociation limit. We found that 1H35Cl in this electronic state has 20 vibrational bound levels, which have energy spacing from 0.35 eV between ν = 0 and 1 to 0.03 eV between ν = 19 and 20. The first electronic excited state has a Π symmetry and is ∼7.85 eV above the GS at the equilibrium geometry. The PES of this state is repulsive and presents the same dissociation limit as the GS. Therefore, as the internuclear distance increases, the two curves get closer in energy. As already previously mentioned, this is a limitation in the application of RCAP method for controlling the vibrational state of the molecule. The dipole transition moments used to compute the effective operators αΣ(R) and αΠ(R) are shown in Figure 3. PES and dipole transition moments of HCl are discussed in more detail in ref 19. The nature of the low-lying excited states of HCl is discussed in refs 18 and 20−22. B. XPS Spectra. The inner-shell single ionization crosssection associated with the XPS spectrum can be computed at a time τ as

∑ cνJ,J,M,M (t )χνGS,J ,M (R , θ , ϕ)e−iε f

ν , Jf

ν , Jf t

0

0

0

f

0

(4)

where χν,Jf,M0 (R,θ,ϕ), and εν,Jf are the eigenvectors and eigenvalues of the field-free Hamiltonian in eq 1, respectively. Inserting eq 4 into the time-dependent Schroedinger equation results in a system of first-order coupled differential equations 8133

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configuration interaction level including up to double electronic excitations (CI-SD) using a homemade package. To account for relaxation of the valence orbitals and to obtain accurate transition moments, we included a set of 75 Hartree−Fock orthogonal orbitals optimized for the Cl 2s−1 σ*(2s−1) coreexcited state in the CI active space to describe simultaneously the 1s−1 core-ionized states and the GS. Calculations were performed using a large aug-cc-pCVQZ atomic Cartesian− Gaussian basis set limited to s, p, and d waves centered on the Cl and H atoms.25 The PESs of the three Σ core-ionized states (X, 2, and 3 2Σ+) are shown in Figure 4. The PES of the X2Σ+ state has a

Figure 4. Ab initio PES of the core-ionized HCl states. Only Σ states are reached within the sudden approximation (eq 6). The lowest state converges to H+ + Cl (1s−1, 3p6) in the infinite atomic distance, and the corresponding PES is nearly parallel to that of the ground electronic state. The two higher states converge asymptotically to H + Cl+ (1s−1, 3P) and H + Cl+ (1s−1, 1P). The corresponding PESs are both repulsive.

Figure 3. Ab initio electronic dipole transition moments as functions of the interatomic distance for the transitions between the ground state and the Σ excited states (lower panel) and between the ground state and the Π excited states (top panel). These dipole transition moments were used to compute the effective coupling operators (eq 2).

σ T(BE, τ ) ∝

minimum located at around R = 1.27 Å, which is ∼4.46 eV below the dissociation limit. This PES is similar to that of the electronic GS. In the infinite atomic distance limit, the X2Σ+ corresponds to H+ + Cl(1s−1 3p6). The PESs of the two higher states (2 and 3 2Σ+) are repulsive. These states correspond in the asymptotic limit to H + Cl+ (1s−1, 1P) and H + Cl+ (1s−1, 3 P), respectively. The dipole transition moments of these states, shown in Figure 5, exhibit different behavior as a function of

∑ e−BJ (J + 1)/kT 0 0

J0 J ,M

∑ j , ν ′ , J ′ , ν , J , M0

|cν0, J , M00(τ )|2 |⟨?νj

2 |+ (R )|? GS ν , J , M 0⟩| ′ , J ′ , M0 j 2 2 (BE − IPj + ενj , J − ενGS , J ) + Γ c /4 ′ ′

(5)

where B is the rotational constant of HCl taken equal to 10.2 cm−1, T is the temperature, and k is the Boltzmann constant. The ionization potential of the adiabatic transition to the coreionized state j is denoted IPj and the binding energy BE = ℏωX − EP is introduced as the difference between the X-ray photon (ℏωX) and the photoelectron (EP) energies. The width (Γc ≈ 0.65 eV) corresponds to the Cl 1s−1 core hole lifetime (∼1 fs).23 The electronic dipole transition moment + j is evaluated within the sudden approximation24 N−1 +j(R ) = ⟨ϕc(E)|z|1s⟩⟨ΨNj − 1|ΨGS ⟩

(6)

where the first term corresponds to the transition dipole moment from inner shell 1s to continuum ϕc(E) orbital. It is assumed constant over the energy range. The second term is the overlap between (N − 1) electronic wave functions of the GS and of the jth state of the 2Σ core-ionized manifold. The PESs of the core-ionized electronic states and the corresponding dipole transition moments were computed as in ref 12. In brief, they were computed at the post Hartree−Fock

Figure 5. Electronic dipole transition moments as a function of the interatomic distance for the transition between the ground state and the Σ core-ionized states computed within the sudden approximation. 8134

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the interatomic distance. Around the equilibrium distance of HCl, the dipole transition moment of the X2Σ+ is maximum and decreases to zero in the asymptotic limit. On the contrary, the dipole transition moments of the two other states are small around the equilibrium distance and increase at larger distances. We can already anticipate that as the molecule climbs the vibrational ladder, the contribution of the X2Σ+ state to the XPS spectra should decrease and that of 2 and 3 2Σ+ states should increase.

III. RESULTS AND DISCUSSION Laser parameters must be chosen carefully such that efficient population transfer is achieved. We fixed both laser intensities to I = 5 × 1012 W·cm−2 and the Stokes photon energy to ωs = 1.17 eV. Such an intensity can be experimentally reached and is low enough for the multiphoton ionization to be negligible. The chosen Stokes photon energy corresponds to a Nd:YAG laser wavelength. The two last parameters, chirp rate cr and initial pulsation of the pump pulse ωi, must be optimized. The RCAP process is based on two-photon transitions and leads to the selection rule on the rotational quantum number ΔJ = 0,±2. In our lasers configuration, there is no transition between different M quantum numbers ΔM = 0. Owing to the chirp of the pump pulse, the first resonant transition reached is ΔJ = +2. To keep selectivity in the RCAP process, it is necessary to optimize the chirp rate cr such that complete population inversion is achieved between (ν,J) and (ν + 1,J + 2) states before the next resonant transition ΔJ = 0 is approached. If the population transfer is not complete between (ν,J) and (ν + 1,J + 2) states, a transition between (ν,J) and (ν + 1,J) at later time may happen simultaneously with a transition between (ν + 1,J + 2) and (ν + 2,J + 4). This situation leads to a loss of control on the vibrational level. The second laser parameter to be optimized, that is, the initial pulsation of the pump pulse, ωi, must be chosen such that initially the energy difference between the two photons (Stokes and pump) is larger than the energy spacing between (ν = 0, J0) and (ν = 1, J0 + 2) states. Furthermore, ωi must be fixed such that this criterion is verified for all J0 initial states populated at the temperature T considered in the present study. We simulated the RCAP process at different temperatures up to 300 K for which population of states above J0 = 10 (see Figure 6) are negligible. We therefore optimized the ωi parameter for J0 = 10, which ensures that RCAP remains efficient for lower J0 values. We found that ωi = 1.574 eV and cr = 1.12 × 10−6 eV fs−1 are the optimal parameters. A. RCAP for T = 0K. In the limit of T = 0 K, the only populated rovibrational level is (ν = 0,J0 = 0). This situation is close to what is encountered in supersonic gas jet experiments. We simulated the RCAP process starting from this rovibrational level. The population of all rovibrational levels were computed as a function of time. Only the most populated ones, which correspond to (ν, J = 2ν, for ν = 0,9), are shown in Figure 7. There is a long plateau up to t = 40 ps, where the system stays in the (ν = 0, J = 0) level. This is due to the choice of ωi = 1.574 eV, which was optimized for a J0 = 10 initial level. The plateau can be shortened by choosing a smaller ωi such that the resonance between (ν = 0, J = 0) and (ν = 1, J = 2) is reached faster. After the long plateau, transitions between (ν,J) and (ν + 1, J + 2) take place up to (ν = 9, J = 18) with a probability of ∼60%. As discussed above, for higher excited levels, the first

Figure 6. Maxwell−Boltzmann distributions of the first rovibrational levels of HCl at T = 80 and 300 K.

Figure 7. Rovibrational level population of HCl as a function of time during the RCAP process for (ν = 0, J0 = 0) initial level.

electronic excited state can be populated via one-photon transition and the RCAP process breaks down. Populations of the rovibrational levels are shown while the laser pulses are still on. We checked that turning off the laser pulses within a few femtoseconds at a given time does not significantly affect the populations. At low temperature, it is therefore possible to prepare selectively HCl in any vibrational level up to ν = 9 by choosing appropriately the laser pulse duration. B. RCAP for Different Temperatures. In the case of gasphase experiments performed at liquid nitrogen (T ≈ 80 K) or room (T ≈ 300 K) temperature, several rovibrational levels are populated initially. Assuming a Maxwell−Boltzmann distribution, the populations at T = 80 and 300 K of the first rovibrational levels are shown in Figure 6. At T = 80 K, the distribution is maximal for J = 1 and is negligible for J greater than 6. At the highest temperature considered (T = 300 K), the distribution is maximal for J = 3 and is negligible for J greater than 10. We, therefore, performed the RCAP simulation for different initial rovibrational levels from (ν = 0, J0 = 0) to (ν = 0, J0 = 10). The populations of the rovibrational levels (ν, J = 2ν + J0, for ν = 0, 9) were computed as a function of time. Results for M0 = 0 are first shown in Figures 8 and 9. 8135

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transitions between the successive levels take place at different times depending on the initial rovibrational level. For example, for (ν = 0, J = 0), the first transition occurs at t = 40 ps, whereas it takes only ∼20 ps for (ν = 0, J = 5) to undergo the first transition. It is then clear that due to the initial rovibrational distribution, there is at any time a distribution of different excited rovibrational levels and the selectivity on the rovibrational state is partially lost at high temperature. However, for high vibrational levels (ν = 8 to 9), it is possible to find laser pulse durations (indicated by dashed lines in Figure 8) such that selectivity is regained because there is one preferentially populated level at these times. Results for different M0 values are now discussed. For a given J0 rotational quantum number there are (2J0 + 1) equally populated M0 states. The transition energies between successive rovibrational levels are M-independent, but the coupling between the levels through the lasers does depend on this quantum number.26 The population of the rovibrational levels during the RCAP process for J0 = 3 and M0 = 0−3 is shown in Figure 10. The transitions from a given (ν,J) to (ν +

Figure 8. Rovibrational level population of HCl as a function of time during the RCAP process for different (ν = 0, J0) initial levels.

Figure 10. Rovibrational level population of HCl as a function of time during the RCAP process for (ν = 0, J0 = 3, M0 = 0−3) initial levels.

1, J + 2) states take place at the same time for all M0 values, but it is seen that the larger M0, the less efficient the population transfer. For example, for J0 = M0 = 3, the population transfer is only ∼40% from (ν = 0, J = 3) to (ν = 1, J = 5) compared with 90% for M0 = 0. Note that after the first (ν = 0, J = 3) to (ν = 1, J = 5) transition the population of the former drops again. For instance, for J0 = M0 = 3, the population of the level (ν = 0, J = 3) decreases from 0.6 to 0.4 at ∼50 ps. This decrease corresponds to transition to (ν = 1, J = 3). Indeed, as discussed above, when the population transfer is not complete for the transitions (ν,J) → (ν + 1, J + 2), other transitions like (ν,J) → (ν + 1,J) can take place at a later time. The populations of (ν,J0) are shown in dashed lines in the Figure, demonstrating such transitions.

Figure 9. Rovibrational level population of HCl as a function of time during the RCAP process for different (ν = 0, J0) initial levels.

It is seen that RCAP is efficient for all initial rovibrational levels, but owing to the rovibrational structure of the molecule, 8136

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C. XPS Spectra. We first discuss the XPS spectra for T = 0 K, which are shown in Figures 11 and 12. The XPS spectra

band B can therefore be used to determine the populated vibrational level. At T = 80 and 300 K, we have a distribution of rovibrational levels; it is therefore not possible to select times when the population of one vibrational level is maximum. To compare with XPS at T = 0 K, we computed XPS spectra at the same times as those selected for the T = 0 K case. XPS spectra in the region of the satellite band, which is characteristic of the rovibrational level, at T = 80 and 300 K are shown in Figures 13 and 14, respectively.

Figure 11. XPS spectra at different times in the main peak region for T = 0 K. From bottom to top, the times are 0, 43, 45, 51, 56, 63, 69, 76, 86, and 100 ps. The choice for these values is explained in the text.

Figure 13. Same as in Figure 12 for T = 80 K.

Figure 12. Same as in Figure 11 but in the region of the satellite band (2832−2846 eV).

were computed at different times during the RCAP process when the population of one vibrational level was maximum (t = 0, 43, 45, 51, 56, 63, 69, 76, 86, and 100 ps). The XPS of HCl in the Cl(1s−1) region (2820−2850 eV) presents two bands: (i) the narrow main peak (denoted M) corresponds to the X1Σ+ → X2Σ ionization threshold energy (BE = 2829.8 eV27); (ii) the broader and less intense satellite band (denoted B) at a BE above 2832 eV is assigned to X1Σ+ → (2,3)2Σ transitions. For ν = 0, it is located at BE = 2844 eV. In Figure 12, for clarity we show only the region of the satellite band. The two XPS bands display significantly different evolutions. The main peak position (M) is roughly independent of the vibrational level of electronic GS, while the satellite band is red-shifted toward low binding energies when increasing the vibrational level, converging to ∼2835 eV, close to the peak M. It should also be noted that the intensity of the peak (M) decreases when increasing ν, while the band (B) exhibits opposite behavior. This behavior is a direct consequence of the R dependence of the dipole transition moments, discussed above, and has been explained in ref 12. The band B is therefore characteristic of the vibrational level of the GS. The position of the maximum of the

Figure 14. Same as in Figure 13 for T = 300 K.

At T = 80 K, the evolution of the spectra as a function of time is similar to that obtained at T = 0 K. However, the maximum of the band at a given time is red-shifted. What is actually observed is mainly the population transfer during the RCAP process for (ν = 0, J0 = 1) because the Maxwell− Boltzmann distribution is dominated by this rotational level. For the initial (ν = 0, J0 = 1) level, the population transfer between successive levels takes place at earlier time compared with (ν = 0, J = 0). At T = 300 K, the characteristic band B is blurred. The selectivity with respect to the time and consequently to the vibrational level is partially lost. It is, however, regained for higher vibrational levels (t = 86 and 100 ps). 8137

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(13) Légaré, F.; Chelkowski, S.; Bandrauk, A. D. Preparation and Alignment of Highly Vibrationally Excited Molecules by CARPChirped Adiabatic Raman Passage. Chem. Phys. Lett. 2000, 329, 469− 476. (14) Press, W. H.; Flannery, B. P.;Teukolsky, S. A.; Vetterling, W. T. Numerical Recipes; Cambridge University Press: New York, 1989. (15) Weiss, M. J.; Lawrence, G. M.; Young, R. A. Photoelectron Spectroscopy of HCl and DCl Using Molecular Beams. J. Chem. Phys. 1970, 52, 2867−2870. (16) (a) Woon, D. E.; Dunning, T. H., Jr. Gaussian Basis Sets For Use in Correlated Molecular Calculations. III. The Atoms Aluminum Through Argon. J. Chem. Phys. 1993, 98, 1358−1371. (b) Dunning, T. H., Jr. Gaussian Basis Sets For Use in Correlated Molecular Calculations. I. The Atoms Boron Through Neon and Hydrogen. J. Chem. Phys. 1989, 90, 1007−1023. (17) Schmidt, M. W.; Baldridge, K. K.; Boatz, J. A.; Elbert, S. T.; Gordon, M. S.; Jensen, J. H.; Koseki, S.; Matsunaga, N.; Nguyen, K. A.; Su, S.; et al. General Atomic and Molecular Electronic Structure System. J. Comput. Chem. 1993, 14, 1347−1363. (18) Bettendorff, M.; Peyerimhoff, S. D.; Buenker, R. J. Clarification of the Assignment of the Electronic Spectrum of Hydrogen Chloride Based on Ab Initio Cl Calculations. Chem. Phys. 1982, 66, 261−279. (19) Engin, S.; Sisourat, N.; Carniato, S. Ab Initio Study of LowLying Excited States of HCl: Accurate Calculations of Optical ValenceShell Excitations. J. Chem. Phys. 2012, 137, 154304-1−154304-7. (20) Van Dishoeck, D. F.; Van Hemert, M. C.; Dalgarno, A. Photodissociation Processes in the HCl Molecule. J. Chem. Phys. 1982, 77, 3693−3702. (21) Ginter, D. S.; Ginter, M. L. Electronic Spectra and Structure of the Hydrogen Halides: Characterization of the Electronic Structure of HCl Lying Between 82 900 and 93 500 cm−1 above X1Σ+. J. Mol. Spectrosc. 1981, 90, 177−196. (22) (a) Green, D. S.; Bickel, G. A.; Wallace, S. C. (2 + 1) Resonance Enhanced Multiphoton Ionization of Hydrogen Chloride in a Pulsed Supersonic Jet: Spectroscopic Survey. J. Mol. Spectrosc. 1991, 150, 303−353. (b) Green, D. S.; Bickel, G. A.; Wallace, S. C. (2 + 1) Resonance Enhanced Multiphoton Ionization of Hydrogen Chloride in a Pulsed Supersonic Jet: Spectroscopy and Rydberg - Valence Interactions of the 1Σ+(0+) and 3Σ−(1, 0+) states. J. Mol. Spectrosc. 1991, 150, 354−387. (c) Green, D. S.; Bickel, G. A.; Wallace, S. C. (2 + 1) Resonance Enhanced Multiphoton Ionization of Hydrogen Chloride in a Pulsed Supersonic Jet: Vacuum Wavenumbers of Rotational Lines With Detailed Band Analysis for Excited Electronic States of H35Cl1. J. Mol. Spectrosc. 1991, 150, 388−469. (23) Krause, M. O.; Oliver, J. H. Natural Widths of Atomic K and L Levels, Kα X-Ray Lines and Several KLL Auger Lines. J. Phys. Chem. Ref. Data 1979, 8, 329−338. (24) Manne, R.; Åberg, T. Koopmans’ Theorem for Inner-Shell Ionization. Chem. Phys. Lett. 1970, 7, 282−284. (25) Kavčič, M.; Ž itnik, M.; Bučar, K.; Mihelič, A.; Carniato, S.; Journel, L.; Guillemin, R.; Simon, M. Electronic State Interferences in Resonant X-Ray Emission after K-Shell Excitation in HCl. Phys. Rev. Lett. 2010, 105, 113004-1−113004-4. (26) Bethe, H. A.; Salpeter, E. E. Quantum Mechanics of One- and Two-Electrons Atoms; Dover: New York, 1957. (27) Bodeur, S.; Marechal, J. L.; Reynaud, C.; Bazin, D.; Nenner, I. Chlorine K Shell Photoabsorption Spectra of Gas Phase HCl and Cl2 Molecules. Z. Phys. D 1980, 17, 291−298.

IV. CONCLUSIONS In conclusion, we presented results on a new scheme combining RCAP technique with XPS. We discussed in detail the RCAP process in the HCl molecule. It was shown that using this technique HCl molecule can be prepared in a welldefined vibrational level up to ν = 9. Effects of the temperature on the RCAP process were investigated. It was demonstrated that higher selectivity is obtained at lower temperatures. XPS during the RCAP process was computed. It was shown that XPS is a powerful tool to probe the rovibrational state of HCl molecule and can be used to follow the population transfer during the RCAP process. Influence of the temperature on the XPS spectra was also investigated. It should be noted that X-ray spectroscopies can be used as diagnostic tools not only for adiabatic passage methods but also for any coherent or optimal control schemes. These spectroscopies should exhibit higher capabilities than other probes for large molecules where the chemical site selectivity will be a great advantage.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel: 0033144276626. Notes

The authors declare no competing financial interest.

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REFERENCES

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