The Predissociation Mechanism for2Σ+Rydberg States of CaCl (original) (raw)
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The Journal of Chemical Physics, 2003
A strong enhancement of absorption to the lowest 2 A 1 state is observed for vibrationally excited chloromethyl radicals. It is demonstrated that this enhancement is due to a significant increase in both electronic and vibrational Franck-Condon factors. Electronic structure calculations of potential energy surfaces ͑PESs͒ and transition dipole moments for the ground and the two lowest excited states of A 1 symmetry, the 1 2 A 1 valence and 2 2 A 1 Rydberg states, reveal the origin of this effect. The shelflike shape of the 1 2 A 1 PES in the Franck-Condon region and the strong dependence of the electronic transition dipole moment on C-Cl distance are responsible for the enhancement. Analysis of the shape of the electron density distribution demonstrates that Rydberg-valence interaction in the two lowest excited states causes the changes in the shape of PESs and transition dipoles with C-Cl distance.
Separation of Long-Range and Short-Range Interactions in Rydberg States of Diatomic Molecules
Journal of Chemical Physics, 128, 194301 (2008)
Observation and analysis of the f͑ᐉ =3͒, g͑ᐉ =4͒, and h͑ᐉ =5͒ Rydberg series of CaF in the range 13ഛ n ഛ 17 is presented. Simultaneous analysis of the f, g, and h Rydberg series of CaF, combined with significant improvements to the long-range model for nonpenetrating Rydberg states, provides a generally applicable scheme for separating the effects of the long-range ͑electric multipole and polarization͒ and short-range ͑core penetration͒ interactions between the Rydberg electron and ion core in diatomic molecules. Techniques for rigorous assignment of nonpenetrating states, as well as extensions of the long-range model, are discussed. Explicit formulas for the first-and second-order matrix elements of the first four anisotropic electric multipole interactions ͑electric dipole, quadrupole, octupole, and hexadecapole͒ are given. The discrepancies between the observed behavior and that predicted by the long-range model, which are particularly significant for the f series, are shown to be due to penetration of the Rydberg electron wavefunction within the ion core. We show that these penetration effects can be understood within the framework of ligand field theory and conclude with a discussion of the relative contributions of the long-and short-range interactions to the quantum defects of the core-penetrating "s," "p," and "d" series of CaF.
Journal of Molecular Spectroscopy, 2017
Mass resolved resonance enhanced multiphoton ionization (REMPI) spectra of a mixture of DCl and HCl were recorded for two-photon resonance excitation in the region of 80 500-89 500 cm À1. Spectra due to resonance transitions to rovibrational states of number of Rydberg and ion-pair states of DCl, were identified and assigned. Five new spectral bands due to transitions to Rydberg states and eight new bands due to transitions to vibrational states of the ion-pair state were identified and analysed to derive energetic parameters. Irregularities observed in vibrational energy level spacing, rotational constants and isotope shifts of chlorine isotopologues from what to expect for unperturbed states, as well as relative signal intensities, are indicative of strong homogeneous interaction between the E 1 R + Rydberg state and the V 1 R + ion-pair state. These observations are found to be due to level-to-level interaction between E and V rovibrational states of same J 0 quantum numbers. Comparison of the data for DCl and HCl is performed.
Chemical Physics, 1995
Two striking examples of Rydberg/ion-pair state coupling have been observed in the spectrum of 12 in the regions 62500-64000 and 56500-59500 cm -~. The coupling is of intermediate strength and the (2+1) REMPI spectra of the resonant Ry ~ X transitions have ion-pair satellites around each Rydberg vibrational level from which they have borrowed intensity. The Rydberg states are identified as the [2II3/2]o7s;lg and [2II3/z]c5d;2g and the ion-pair states as the/31g and D'2g. Curve crossings occur close to the v' = 532 level of the/3 state and v' = 311 of the D' state respectively. The spectra are modelled by solving the two-state coupling problem in adiabatic basis and in order to deduce approximate values of the coupling matrix elements, extrapolations of the known portions of the potential energy curves of the Big and D'2g ion-pair states are necessary. The diagnostic value of the magnitude of the electronic part of Rydberg/ion-pair coupling matrix elements in probing the electronic configuration of ion-pair states at short range is discussed. 0301-0104/95/$09.50 ~) 1995 Elsevier Science B.V. All rights reserved SSD10301-0104(95)
Journal of Molecular Spectroscopy, 1981
The electronic absorption spectrum of cyanogen chloride has been investigated in the range 2200-1250 A. The first s-Rydberg transitions, .%'Z'-* %, and B'Z' + 'II, have been assigned, and analyzed to yield exchange and spin-orbit coupling parameters. The relative intensities of these two transitions have been shown to accord with an intermediate coupling situation. The P + ?y* intravalence excitations, leading to '.VY-, A and 2') states, have been discussed. It has been shown that one or both of the 'I-and 'A states have bent geometries and that the IX+ state is located (tentatively) at 79 755 cm-'. Two o + r*/r + CT* states have been assigned, one at 56 340 cm-', the other at 74 450 cm-'. The latter assignment is tentative, being largely based on observed vibronic interferences between the X'I' + 'II, transition and the 74 450 cm-' transition. A considerable amount of vibrational oscillator strength and quantum defect data is presented.
Evidence for a non-Rydberg molecular doubly excited state of Ca2
Chemical Physics Letters, 2009
We report experimental and theoretical evidence of a non-Rydberg molecular doubly excited state of Ca 2 involving excited molecular orbitals mixing 4p and 3d characters. The excitation spectrum of Ca 2 , carried by helium or argon clusters, is recorded experimentally in the range 25600-27800 cm −1 , displaying a bimodal structure. The latter is interpreted from ab initio calculation and analysis of the adiabatic states of Ca 2 up to doubly excited asymptotes Ca(4p3d 1 D)+Ca(4s 2 1 S) and Ca(4s3d 3 D)+Ca(4s4p 3 P), and the relevant dipole transition moments. The bimodal structure is assigned as resulting from the avoided crossing between adiabatic states 3 1 Π u and 4 1 Π u , reflecting the mixing of doubly excited configurations and absorbing singly excited configurations.
A critical re-assignment of the Rydberg states of iodomethane based on new polarization data
The Journal of Chemical Physics, 2013
2-and 3-photon excitation of components of the lower Rydberg states of iodomethane (CH 3 I) using linearly and circularly polarized light, followed by ionization with one more photon, is used to determine their molecular term symbol, , values as well as quantum defects. These values, together with a detailed theoretical analysis, require a re-assignment of the 7s and 8s states to various components of the 5d and 6d states, but there is evidence of (n+2)s/nd hybridization in the pairs of = 1 states. Predissociation sets in for all Rydberg states beyond 6d based on the ground ( 2 3/2 ) state of the core, but sharp autoionizing resonances based on the 2 1/2 core state are assigned to the 9s, 7d , and 5f states. The dominant effect of the singlet/triplet character of the Rydberg states on their accessibility from the ground state, seen in bromomethane and chloromethane, is again apparent and a concordant interpretation of the Rydberg spectra of CH 3 I can now be presented. Evidence for coupling of some = 1 and = 0 + Rydberg states with a repulsive valence state and an ion-pair state, respectively, is also put forward.
The Journal of Chemical Physics, 1999
For the nf (lϭ3) series of Na 2 , quantum defects are calculated from theoretical values of the core quadrupole moment and polarizabilities. They compare favorably with those inferred from our preliminary report of high resolution all-optical triple resonance spectroscopy ͓Chem. Phys. Lett. 236, 553 ͑1995͔͒ and from the full report of such spectra given here. The spectrum is the simplest when the higher intermediate state has JЈϭ0 which requires a final state Jϭ1. We predict the stroboscopic effect should first occur when nϭ52 for the nf series, as we observe, rather than at nϭ69 for the np series. Our data thus confirm that the strongest series is the nf. Hence the ionization potential is not 39 478.75Ϯ0.04 cm Ϫ1 as previously reported, but rather 39 478.101Ϯ0.013 cm Ϫ1 , implying a molecular ion dissociation energy of D 0 0 (Na 2 ϩ )ϭ7914.038Ϯ0.014 cm Ϫ1 .
Journal of Physics B: Atomic, Molecular and Optical Physics, 1992
Using a two-step laser optogalvanic technique in a Ca DC discharge the authors have measured the energies of the even 3dnd J=0 and J=2 as well as some 3dng J=2 autoionizing states of Ca in the range below 62500 cm-1, for which calculations have been published. In general the agreement between experimental and theoretical values is very good. Especially important is the detection of the '4p2'1S0 and, probably, the 4p5p3D2 perturbers.
Spectroscopy and dynamics of the predissociated, quasi-linear S2 state of chlorocarbene
The Journal of chemical physics, 2012
In this work, we report on the spectroscopy and dynamics of the quasi-linear S 2 state of chlorocarbene, CHCl, and its deuterated isotopologue using optical-optical double resonance (OODR) spectroscopy through selected rovibronic levels of the S 1 state. This study, which represents the first observation of the S 2 state in CHCl, builds upon our recent examination of the corresponding state in CHF, where pronounced mode specificity was observed in the dynamics, with predissociation rates larger for levels containing bending excitation. In the present work, a total of 14 S 2 state vibrational levels with angular momentum = 1 were observed for CHCl, and 34 levels for CDCl. The range of in this case was restricted by the pronounced Renner-Teller effect in the low-lying S 1 levels, which severely reduces the fluorescence lifetime for levels with K a > 0. Nonetheless, by exploiting different intermediate S 1 levels, we observed progressions involving all three fundamental vibrations. For levels with long predissociation lifetimes, rotational constants were determined by measuring spectra through different intermediate J levels of the S 1 state. Plots of the predissociation linewidth (lifetime) vs. energy for various S 2 levels show an abrupt onset, which lies near the calculated threshold for elimination to form C( 3 P) + HCl on the triplet surface. Our experimental results are compared with a series of high level ab initio calculations, which included the use of a dynamically weighted fullvalence CASSCF procedure, focusing maximum weight on the state of interest (the singlet and triplet states were computed separately). This was used as the reference for subsequent Davidson-corrected MRCI(+Q) calculations. These calculations reveal the presence of multiple conical intersections in the singlet manifold.