States Of HCl Research Articles

Theoretical MRCI + Q study on electronic structure and spectroscopic properties of the HX+(X = F, Cl, Br, I) cations

In this work, we have systematacially investigated the electronic structure and spectroscopic properties of the HX+ (X = F, Cl, Br, I) cations by using the highly correlated MRCI + Q approach. This is the first comprehensive ab initio study on the electronic states of the HX+ cations. The spin–orbit coupling (SOC) effect is introduced with the state interaction approach. There are total 10 Λ-S and 18 Ω states obtained in the calculation. The results show that the potential energy curves’ (PECs) shapes and structure of the electronic states of different HX+ cations exhibit the significant distinction due to the X-dependent energy-level order of the unique dissociation channel H+(1Sg) + X(2Pu). From PECs, the spectroscopic constants of the bound electronic states are determined, which are in good agreement with available observed values. Regarding HBr+ and HI+, the good agreement has been achieved only when the SOC effect is considered. The predissociation for the first excited A2Σ+ state of HCl+, HBr+, and HI+ is analyzed based on computed spin–orbit matrix elements. Around the equilibrium position, the energy splittings of X2Π are calculated to be 288, 661, 2691, and 5137 cm−1 for HF+, HCl+, HBr+, and HI+, respectively. It has been demonstrated that SOC is substantial for HX+, leading to significant changes in PECs’ shapes as well as in electronic structure. Finally, the transition properties are predicted, including transition dipole moments, Franck–Condon factors, and radiative lifetimes. Both the Ω transitions A2Σ+ 1/2-X2Π3/2 and A2Σ+ 1/2-X2Π1/2 of the HX+ cations are determined to possess the radiative lifetimes at the microsecond (µs) level.

Stereodynamics of the Ca + HCl → CaCl + H molecular reaction imposed by the rotational‐excited states of HCl

AbstractThe effects of the initial rotational‐excited states of the HCl molecule on the stereodynamics properties of the Ca + HCl molecular reaction are investigated using the quasiclassical trajectory theory and the analytical potential energy surface. The orientation and alignment behaviors for the rotational angular momentum of the product, along with the generalized differential cross section (PDDCS)‐dependent polarization, are calculated to explore the stereodynamics properties. The initial rotational‐excited states of the HCl molecule impose a remarkable effect on the vector correlation distributions, regardless of the orientation, alignment, or PDDCS. The forward, backward, and weak sideway scatterings are found in the Ca + HCl → CaCl + H molecular reaction. The results demonstrate that the initial rotational‐excited state of j = 3 results in more obvious stereodynamics effects.

A comment on “Ab initio study: the potential energy curves and ro-vibrational spectrum of low-lying excited states of HCl+ cation”

ABSTRACTSince the 2Π state in HCl+ is an inverted doublet, the energy of the 2Π1/2 state is higher than the 2Π3/2. Therefore, the larger value of intensity correspond to the transition of 2Π3/2. We calculated the Einstein A coefficients and radiation lifetimes for the A2Σ+-X2Π transition. Our results are in good agreement with the experimental data and theoretical values. Then the ro-vibrational line intensities of the 1-0 band were calculated for the 2Π3/2 and 2Π1/2 states of HCl+. Employing the RKR potential, the predicted band origins for Δν=1-0 are 2569.3 and 2568.55 cm-1 for 2Π3/2 and 2Π1/2, respectively.

Ab initio study: the potential energy curves and ro-vibrational spectrum of low-lying excited states of HCl+ cation

ABSTRACTThe potential energy curves (PECs) of 11 electronic states of HCl+ cation are obtained by using the high-level relativistic multi-reference configuration interaction plus Davidson correction (MRCI + Q) method. The spin-orbit coupling effect is also taken into account in electronic structure calculations. The PECs of X2Π and A2Σ+ states accord well with corresponding Rydberg--Klein–Rees PECs. The spectroscopic constants for the bound states of HCl+ agree well with available theoretical and experimental data. The dipole moments (DMs) and transition dipole moment of the X2Π→A2Σ+ are also in agreement with previous results. According to the PEC and DM, we calculated Einstein A-coefficients and ro-vibrational line intensities of 1–0, 2–0, 2–1, 3–0, 3–1, 4–0 and 4–1 bands for X2Π1/2 state.

Erratum: “Ab initio study of low-lying excited states of HCl: Accurate calculations of optical valence-shell excitations” [J. Chem. Phys. 137, 154304 (2012)

Erratum: “<i>Ab initio</i> study of low-lying excited states of HCl: Accurate calculations of optical valence-shell excitations” [J. Chem. Phys. 137, 154304 (2012)

Photoelectron spectroscopic study of the E ⊗ e Jahn–Teller effect in the presence of a tunable spin–orbit interaction. II. Rovibronic analysis of the 2E ground state of CH3CI+

The PFI-ZEKE photoelectron spectrum of the CH3Cl+ E ← CH3Cl transition was recorded in the range 90900–93400 cm−1 following single-photon excitation from the ground state. The spectrum consists of well-resolved spin-vibronic bands, some of which with partially resolved rotational structure, and provides new information on the combined effects of the Jahn–Teller and spin–orbit interaction in the E ground state of CH3Cl+. The analysis of its spin-rovibronic structure reveals a weak linear Jahn–Teller effect along the H3C–Cl bending e mode (ν6) and enabled the derivation of Jahn–Teller coupling constants along ν6, rotational constants, and spin–orbit interaction parameters for the E ground state of CH3Cl+. The Jahn–Teller effect is dynamical in the ground state of CH3Cl+ and the photoelectron spectrum does not provide evidence for a reduction of the molecular symmetry to Cs symmetry. Weak rotational satellite bands were observed in transitions to several excited vibrational levels of CH3Cl+ and interpreted in terms of the spin-rovibronic photoionization selection rule derived in the analysis of the photoelectron spectrum of CH3I (M. Grütter, J. M. Michaud and F. Merkt, J. Chem. Phys. 134, 054308 (2011)). Compared to the ground state of HCl+ ( cm−1), the spin–orbit splitting is strongly reduced to cm−1. The reduction is primarily attributed to an electronic effect and, to a lesser extent, to the quenching of the spin–orbit interaction by the Jahn–Teller effect .

Adiabatic versus diabatic descriptions of the lowest Rydberg and valence $1^\Sigma ^{+}$Σ+1 states of HCl

In this contribution we first report new ab initio self-consistent field configuration interaction calculations of the first excited adiabatic potential of (1)Σ(+) symmetry, the 2(1)Σ(+) or B(1)Σ(+) state, which presents two minima and can thus be seen as made up of the Rydberg E(1)Σ(+) and the valence V(1)Σ(+) states. Based on the computed 2(1)Σ(+) potential, we devised a theoretical procedure to compute the vibronic structure in order to try to explain the energy levels observed in the region above 76 254.4 cm(-1) which display an irregular vibrational structure, indicative of spectral perturbations. We try to find out which representation of the electronic states, the diabatic or the adiabatic one, is best suited to replicate the lowest observed vibronic levels of the E and V states. To this end, we deduce, from the 2(1)Σ(+) potential and its complementary adiabatic potential, two diabatic potentials. We then carry out a coupled equation treatment based on these diabatic potentials. The results of this treatment indicate that, in the present case, the adiabatic representation is better than the diabatic one to describe the observed vibronic levels. This is due, as expected, to the existence of a strong electrostatic interaction between the two diabatic potentials.

Proton formation dynamics in the REMPI[2+n] process via the F Δ12 and f Δ32 Rydberg states of HCl investigated by three-dimensional velocity mapping

HCl in the bulk gas phase at a pressure of 10(-5) mbar has been excited via selected Q-lines of the two-photon transition band systems F (1)Delta(2)<--X (1)Sigma(+)(1,0) [Q(8)], V (1)Sigma(+)<--X (1)Sigma(+)(14,0) [Q(8), Q(7)] and f (3)Delta(2)<--X (1)Sigma(+)(0,0) [Q(2-6)]. Concerning the V<--X excitation, subsequent photon absorption is known to yield HCl(+), H(n=2)+Cl, H(+)+Cl(-) and H+Cl(4s,4p,3d). Vibrationally excited HCl(+) (v(+) > or = 5) can be photodissociated to H(+)+Cl, and excited atoms can be easily photoionized by absorption of a fourth photon, respectively. Using three-dimensional velocity map imaging, the spatial proton velocity distributions resulting from these processes for these particular transitions were studied for the first time. Kvaran et al. [J. Chem. Phys. 131, 044324 (2009); J. Chem. Phys. 129, 164313 (2008)] recently reported a substantial increase in the formation of chlorine and hydrogen ions in single rovibrational transitions of the F (1)Delta(2) and f (3)Delta(2) band systems using mass resolved resonance enhanced multiphoton ionization spectroscopy and explained this by the vicinity of single rovibrational levels of the V (1)Sigma(+) state for which photorupture is the main feature. Thus, the known dissociation dynamics of the V (1)Sigma(+) state should also leave their fingerprint in the spatial proton velocity distribution emerging from the photodissociation of those states. Accordingly, we found a strong increase in the H(+) ion signal for the Q(5) line of the f (3)Delta(2)<--X (1)Sigma(+)(0,0) transition, the extra signal resulting from dissociation into H(n=2)+Cl((2)P(1/2)) and the ion pair. No increase for the HCl(+)(v(+) > or = 5) photodissociation channel or dissociation into H(n=2)+Cl((2)P(3/2)) has been observed. Furthermore, H(+) distributions from the Q transitions of the f (3)Delta(2)<--X (1)Sigma(+)(0,0) band system were found to show the two features previously ascribed to the "gateway" state [(4)Pi...4s](3)Pi(0), i.e., autoionization into HCl(+)(5 < or = v(+) < or = 8) and nonadiabatic dissociation into H(n=2)+Cl((2)P(3/2)). The F (1)Delta(2)<--X (1)Sigma(+)(1,0) band system only showed significant proton formation for the Q(8) line. The speed distribution is the same as for the Q(8,7) lines of the V (1)Sigma(+)<--X (1)Sigma(+)(14,0) transition while the excitation history is conserved in the angular distribution confirming the resonance interpretation.

Time-dependent Quantum Wave Packet Study of F+HCl and F+DCl Reactions

The F+HCl and F+DCl reactions are studied by the time-dependent quantum wave packet method, using the most recent potential energy surface reported by Deskevich et al.. Total reaction probabilities for a number of initial ro-vibrational states of HCl and DCl diatomic moiety are presented in the case of total angular momentum J=0. It is found that for both reactions the initial rotational excitation of the diatomic moiety enhances greatly the reaction probabilities but this effect is more significant for F+HCl system. This is mainly due to larger rotational constant of the HCl reagent. The initial vibrational excitation of the diatomic moiety has little effect on the reactivity for both systems except shifting down the collision energy threshold. The results indicate that the reaction coordinates for these two systems are effectively along rotational freedom degree. More quantum phenomena, such as tunneling and resonance, are observed in F+HCl reaction than F+DCl reaction, and for the initial states studied, the reactivity of the later is lower. Different skewing angles of these two systems account for these isotopic differences.

Interpreting the dynamics of HCl+ dissociation in a strong laser field atλ = 10.3 µm

The strong field dissociation of HCl+ at a wavelength of λ = 10.3 µm is examined in detail, using quantum wavepacket and trajectory methods. Athree-potential-curve treatment, which currently offers the most theoretically completedescription of the molecular dynamics, is used to simulate the dissociation process, and providespredictions of the dissociation probability, electronic branching ratios and kinetic energydistributions. Classical trajectory simulations on a single potential curve (ground state ofHCl+)are used to increase understanding of simulations performed using three potential curves.The impact on predicted product properties of using two potential curves (ground and firstexcited states) versus three potential curves is also explored. The fragment’s kinetic energydistributions are discussed extensively and quantum simulation results interpreted with theaid of classical trajectories as well as simple models such as a wagging potential tailmodel, developed by Thachuk and Wardlaw (1995 J. Chem. Phys. 102 7462). Atunnelling variant of a barrier suppression model, used for predicting the dissociationthreshold, is developed, and shown to be more accurate than previous models.

Three-photon absorption spectroscopy: the L(1Φ3) and m(3II1) states of HCl and DCl

Analysis of (3+1) REMPI room temperature spectra by use of three-photon absorption modelling allowed, for the first time, identification and characterization of Ω = 3, Φ states (L(1Φ3)) in HCl and DCl and of the m(3II1) state in DCl. Simulation analyses and determination of isotope shifts allowed evaluation of vibrational and rotational spectroscopic parameters for both states and both molecules. The mechanism of three-photon absorption in the m(3II1) ← X(1Σ+) transition is discussed.

Quantitative spectral analysis of HCl and DCl in 120–220 nm: Effects of singlet–triplet mixing

Photoabsorption cross sections of HCl and DCl in the spectral region 120–220 nm were measured using synchrotron radiation as a light source. The absorption contour of the A 1Π←X 1Σ+ band of HCl in the 134–195 nm region is slightly asymmetric, whereas that of DCl is symmetric, with wavelength of absorption maximum shifted from ∼153.9 nm for HCl to ∼155.8 nm. The asymmetry in HCl and the atypical direction of shift in peak wavelengths upon deuteration are attributed to singlet–triplet mixing in its ground X 1Σ+ state of HCl; this triplet component contributes to the oscillator strengths of the A–X band of HCl via transition to the repulsive triplet state 1 3Σ+. The small triplet character in HCl is further supported by an observation that the oscillator strength of the (0,0) band for the b 3Π–X 1Σ+ transition of DCl is ∼17% smaller than that of HCl. This triplet component may account for greater values of spin–orbit branching ratios for products, Cl*(2P1/2)/Cl(2P3/2), observed upon photolysis of HCl in the 143–167 nm region. For both HCl and DCl, ratios of observed oscillator strengths to calculated Franck–Condon factors of the C 1Π state decrease with vibrational levels, whereas those of the b 3Π state increases with increasing vibrational levels. Such a variation was attributed to perturbation between the b and C states, for which quantitative data are established in this study.

The Radial Hamiltonians for the X1Σ+ and B1Σ+ States of HCl

All literature vibration–rotational and pure rotational transition energies for the ground X1Σ+ electronic state of H35Cl, H37Cl, D35Cl, and D37Cl, along with the entire collection of electronic B1Σ+ → X1Σ+ emission data for the four isotopomers, have been used in a least-squares fit of compact analytic Born–Oppenheimer potential functions for the B1Σ+ and X1Σ+ electronic states. Additional functions related to the adiabatic and nonadiabatic corrections have also been determined. Separate least-squares fits were made according to the hamiltonian operators of J. K. G. Watson (J. Mol. Spectrosc. 80, 411 (1980)) and R. M. Herman and J. F. Ogilvie (Adv. Chem. Phys. 103, 187 (1998)). The results from the separate analyses demonstrate clearly that the two hamiltonian operators are essentially equivalent, both achieving equally satisfactory representations of the spectral data, and furnishing virtually identical Born–Oppenheimer potential functions. Fully quantum-mechanical vibrational eigenvalues and rotational perturbation series parameters Bv–Ov are presented for the lower levels of the X1Σ+ ground state for which infrared and/or microwave data are available (v" ≤ 7 for H35Cl and H37Cl, v" ≤ 10 for D35Cl and D37Cl). These parameters collectively reproduce the corresponding spectroscopic line positions included in our fit to within the uncertainties of the measurements.

MRCI Calculation, Scaling of the External Correlation, and Modeling of Potential Energy Curves for HCl and OCl

The first lowest 2Π and 2Σ+ states of OCl, as well as the 1Σ+ and 3Σ+ states of HCl, have been calculated at the ab initio MRCI level, and modeled semiempirically using the extended Hartree−Fock approximate correlation energy method. Spectroscopic RKR data and accurate ab initio energies have been used to obtain the model parameters. The vibrational levels of those states have also been calculated, and found to be in good agreement with existing spectroscopic data for the ground electronic states of the title diatomic molecules.

Real time kinetics and thermochemistry of the uptake of HCl, HBr and HI on water ice in the temperature range 190 to 210 K

AbstractThe real time kinetics of adsorption and desorption of HCl on ice have been studied in a very low pressure reactor (Knudsen cell). We used two complementary techniques, namely pulsed valve or transient supersaturation and steady state experiments. The kinetics of adsorption, following a first order rate law, has been found to depend on the number of HCl molecules in a pulse for transient supersaturation and on the HCl partial pressure or flow rate in steady state experiments. The uptake coefficient γ ranges from 0.34 to 0.22 in the temperature range 190 to 210 K for dry adsorption leading to a quasi‐liquid state of HCl on ice and from 0.31 to 0.13 for adsorption leading to a liquid solution of HCl. In both cases a negative temperature dependence for uptake of HCl on ice of −1.8±0.5 and −3.1±0.5 kcal/mol has been observed. In addition, the fraction of HCl that could be retrieved by desorption after dosage with HCl depended strongly on the thermodynamic state of the HCl/ice substrate as well as on the temperature and varied in the range from 10 to 80%. We determined the rate of irreversible surface‐to‐bulk loss, with a limiting rate of 1.0·1013 molecule s−1 cm−2 at 200 K. In addition, we studied the kinetics of adsorption of HBr and HI on ice resulting in γ values similar to HCl. However, ice in the range 190 to 210 K did not support any measurable vapor pressure of both HBr and HI after adsorption of up to several formal monolayers in contrast to HCl.

A semiclassical model of the angular distribution of the photofragments of predissociating molecules

A semiclassical model is introduced for calculating the differential cross section for the dissociation of a molecule in a long-lived state. The model is based on the idea that the angular distribution is a “snapshot” of the excited state wave function, provided that exit channel effects may be neglected. Algebraic expressions are derived for one- and two-photon excitation. The model is compared with velocity-aligned Doppler spectra of Cl atoms produced by the predissociation of various states of HCl.

Competition between direct dissociation and resonant Auger decay: a quasi-classical model applied to the [formula omitted] states of HCl, DCl and Cl 2

Resonant Auger spectra of HCl, DCl, and Cl 2 following the ( Cl 2 p 3 2 → σ ∗ excitation were studied. Both ‘molecular’ and ‘atomic’ Auger transitions are observed and assigned. The branching ratio of ‘molecular’ versus ‘atomic’ Auger transitions increases with increasing reduced mass of the target molecules. Using a quasi-classical model, we are able to deduce the principal Auger lineshape in agreement with experiment. The simultaneous occurrence of ‘atomic’ and ‘molecular’ Auger transitions is shown to be the general case for repulsive intermediate states. The kinematic model successfully describes the mass and lifetime dependence of the competition between the Auger process and dissociation.

Coherent laser control of bound-to-bound transitions of HCl and CO

We have used the method of Shapiro, Hepburn, and Brumer to control the ionization rates of HCl and CO. This method is based on the principle of quantum mechanical interference between two competing paths. In this case the two paths are one- and three-photon excitation of an intermediate Rydberg state. A vacuum ultraviolet (VUV) (110–115 nm) laser beam was produced by third-harmonic generation from an UV beam in Kr gas. The relative phases of the two beams were controlled by passing them through a chamber containing either Ar or H2. The laser beams were focused into a molecular beam, and the ionization products were measured in a time-of-flight mass spectrometer. As the pressure of the phase-tuning gas was varied, the ionization signal was found to oscillate with a period that is proportional to the difference of the indices of refraction of the tuning gas at the UV and VUV wavelengths. We have applied this technique to transitions involving different intermediate electronic states [the j 3Σ−(0+), H 1Σ+(0+), and m 3Π(1) states of HCl and the B 1Σ+ state of CO], different rotational lines of the same electronic transition, and different competing processes (ionization vs dissociation) following excitation of the intermediate state.

Threshold-field-ionization photoelectron spectroscopy and delayed forced autoionization of HCl.

A time-of-flight photoelectron spectrometer is oriented coaxially with a pulsed molecular beam to detect high Rydberg states of HCl with lifetimes as long as 7 \ensuremath{\mu}s. Two classes of such states are found. Delayed extraction following double-resonant excitation field-ionizes Rydberg states of very high principal quantum number (n\ensuremath{\ge}100) that converge to successive rotational limits for producing ${\mathrm{HCl}}^{+}$, effectively yielding a rotationally resolved threshold photoelectron spectrum. Surprisingly, excitation under more rigorously field-free conditions (100 mV/cm) produces additional resonances which can be assigned to series of long-lived Rydberg states extending to principal quantum numbers as low as 10. The lower-principal-quantum-number resonances isolated by their long field-free lifetimes appear to constitute a high-angular-momentum nonpenetrating subset of the autoionizing Rydberg series that converge both to accessible rotational levels of the upper $^{2}\mathrm{\ensuremath{\Pi}}_{1/2}$ threshold and excited rotational limits of the $^{2}\mathrm{\ensuremath{\Pi}}_{3/2}$ ground state of ${\mathrm{HCl}}^{+}$.

Decay channels of core-excited HCl

The HCl 2${\mathit{p}}_{\mathrm{Cl}}$\ensuremath{\rightarrow}${\mathrm{\ensuremath{\sigma}}}^{\mathrm{*}}$ photoexcitation resonance has been studied using a tunable synchrotron radiation beam with a narrow bandwidth. Extensive ab initio molecular and atomic calculations have been carried out to analyze the details of the measured electron spectra. The interatomic potential-energy curves have been calculated for the ground and selected excited states of HCl using the complete-active-space self-consistent-field method. Multiconfiguration Dirac-Fock energies and line intensities of the atomic chlorine Auger spectrum have been used to identify the intense atomic spectral lines in the measured electron spectrum. Comparison between theory and experiment indicates fast neutral dissociation of the excited HCl molecules, followed by resonance Auger processes of the core-excited chlorine atoms. The atomic spectral lines are found to overlap with a strong background of broad structures, which sum up to 40% of the total intensity. This contribution has been addressed to the 2.9-eV potential well in our potential-energy curve of the excited HCl allowing for Franck-Condon transitions to bound vibrational states with a molecular nonradiative decay mode.