Rovibronic Levels Research Articles

A new general Renner-Teller (including ɛ ≳ 1) spectroscopic formalism for triatomic molecules

We present a general approach and its implementation for calculating the rovibronic levels and spectra of rigid or floppy Renner-Teller triatomic molecules, which is not limited in the number and quantum numbers (Λ, S) of electronic states. The case of strong Renner-Teller coupling (ɛ ≳ 1) is specially studied and it is shown that the proposed implementation provides very accurate and stable results for this complicated problem. Few examples (BF(2), HBF, and CCO) illustrate the performance of the code.

Rotational analysis of the Ångström system (B1Σ+–A1Π) in the rare 13C17O isotopologue

Although yet unobserved in the very rare 13C17O isotopologue, the Ångström system (B1Σ+–A1Π) was obtained under high resolution as an emission spectrum using a conventional spectroscopic technique.The emission from the discharge was observed with a plane grating spectrograph and recorded by a photomultiplier tube. In total, 192 transition wave numbers belonging to two bands (0–1 and 0–2) were precisely measured and rotationally analyzed. This method allowed us to determine the merged rotational constants B0=1.8131941(58)cm−1 and D0=5.5620(46)×10−6cm−1 and the individual molecular constant B1=1.471059(47)cm−1, D1=5.315(64)×10−6cm−1, B2=1.451762(13)cm−1, D2=7.812(16)×10−6cm−1 for the as yet unanalyzed 13C17O molecule B1Σ+ and A1Π states, respectively. The band origins σ0-v″ of the Ångström system in the 13C17O molecule were also calculated.Numerous rotational perturbations observed in the A1Π state in 13C17O molecule have been identified and analyzed in detail. The suspected candidates responsible for these irregularities were indicated by means of a graph of the rovibronic levels of the neighboring states based on the estimated term value in the 13C17O molecule. The values of these perturbations have also been defined for both the e- and f-parity of the A1Π(v=1 and 2) state. Simultaneously, the B1Σ+ state was observed to be quite regular up to the observed Jmax level.

Spectroscopic prescription for optimal stimulated Raman transfer of ultracold heteronuclear molecules to the lowest rovibronic level

We show that the multiplicative product of a molecular-beam excitation spectrum and an ultracold-molecule excitation spectrum, with a frequency offset appropriate to the initial ultracold-molecule level, provides the relative rate of stimulated Raman transfer (SRT) from a given high rovibrational level to the lowest rovibronic level, i.e., the ${v}^{\ensuremath{'}\ensuremath{'}}=0,{J}^{\ensuremath{'}\ensuremath{'}}=0$ level of the ground electronic state for photoassociated (and magnetoassociated) ultracold molecules. This product spectrum clearly indicates the optimal pathways for SRT, even when the two component spectra are completely unassigned. We illustrate this specifically for the case of KRb.

Accurate quantum mechanical study of the Renner-Teller effect in the singlet CH2

The Renner-Teller (RT) effect between the two low-lying electronic states of singlet CH(2), ã(1)A(1) and b̃(1)B(1), is studied using the multi-configuration time-dependent Hartree method with complete treatment of the RT terms. The RT terms, which are the matrix elements of the electronic orbital angular momentum operators, are calculated with ab initio methods and fitted to analytical functions. The ro-vibronic energy levels with complete treatment and constant approximation of the RT terms are calculated and compared. The influences of the geometry dependence of the RT terms on the ro-vibronic energy levels are discussed. The differences of the variation trends and influences of the RT terms between CH(2) and NH(2) are explored. In particular, as the molecule bends from linearity, the curve of the RT term (<linear span>ã(1)A(1)|L(z)(2)|ã(1)A(1)(<linear span>) first goes down to reach a minimum and then goes up leading to decreased zero point energy and bending energy levels for the lower state of CH(2) in contrast to the case of NH(2).

Time-sliced velocity-mapped imaging studies of the predissociation of single ro-vibronic energy levels of N2 in the extreme ultraviolet region using vacuum ultraviolet photoionization

The predissociation of N(2) from the rotational levels in the o(1)∏(u) (v(') = 2) and b(') (1)Σ(u) (v(') = 8) bands has been studied in the wavenumber (or energy) range from 109 350 cm(-1) (13.5577 eV) to 109 580 cm(-1) (13.5862 eV) by time-sliced velocity-mapped imaging technique with VUV photoionization detection of the fragments. These levels were excited from the ground state of N(2) (X(1)Σ(g) (+), v(") = 0) levels using an unfocused vacuum ultraviolet (VUV) laser via a one-photon process. The same VUV laser is used to ionize the metastable N ((2)D(o)) produced from the predissociation process and the time-sliced velocity-mapped imaging technique is used to determine their velocity and angular distributions. Two different theoretical methods developed, respectively, by Kim et al. [J. Chem. Phys. 125, 133316 (2006) and Zande [J. Chem. Phys. 107, 9447 (1997)] were used to calculate the anisotropic parameters for the predissociation to the channel N((4)S(o)) + N((2)D(o)) to compare with the observed value for each of the rotational levels. Very good agreement with the experimental results was obtained for both methods. Possible predissociation mechanisms were predicted from the measurements and calculations.

Dipole moment functions of the iodine D′2g –A′2u, , D0+u–X0g+ and transitions

The dipole moment functions of the iodine and transitions in the ranges of 3.0–4.8 and 3.1–4.1 Å have been determined for the first time by means of simulation of the luminescence spectra from the D′, vD′ = 58, JD′ = 39 and D, vD = 13, 18; JD = 26 rovibronic levels, respectively. The dipole moment functions of the iodine and transitions have also been re-examined using a more perfect than employed earlier method of calibration of the spectral sensitivity function of the condenser/monochromator/detector system.

Ab initio study of vibronic coupling in the ozone radical cation

The rovibronic levels of the X ˜ 2 A 1 and A ˜ 2 B 2 electronic states of O 3 + have been calculated variationally for the first time, using high-level (ICMRCI/cc-pcV5Z) ab initio diabatic potential energy surfaces which explicitly consider the non-adiabatic interaction between the two states. Vibronic levels for J = 1/ 2, 3/ 2 have been calculated and assigned for energies up to 2000 cm −1 above the ground state, making comparisons with recent results from ZEKE photoelectron experiments of ozone. The procedure has good predictive capabilities and it is used to confirm previous assignments and to tentatively identify some unassigned features in the low energy part of the O 3 + spectrum.

The high sensitivity absorption spectrum of ozone ( 18O 3 and 16O 3) near 7800 cm −1: Identification of the 3A 2(0 0 0)–X(1 1 0) hot band superimposed to very weak vibrational bands

The very weak absorption spectra of 18O 3 and 16O 3 have been recorded between 7700 and 7920 cm −1 by high sensitivity cavity ring down spectroscopy ( α min ∼10 −10 cm −1). The upper limit of the investigated region is only 6% below the dissociation energy. The spectrum consists in the superposition of very weak vibrational bands and unexpected broad absorption features which dominate in the case of the 18O 3 isotopologue. From recordings at temperatures ranging from 294 to 354 K, the broad features were identified as due to the 3A 2(0 0 0)–X 1A 1(1 1 0) hot band. The rovibronic levels of the 3A 2(0 0 0) state are predissociated and the widths of the corresponding lines range from 0.02 to at least 0.5 cm −1.

Extended permutation-inversion groups for simultaneous treatment of the rovibronic states of trans-acetylene, cis-acetylene, and vinylidene

The electronic ground state potential surface of acetylene (H C C H) has a minimum at the linear conformation, but the excited electronic states may have potential minima at a variety of nonlinear equilibrium shapes. This work is concerned with the group theoretical ideas necessary to treat simultaneously the symmetry properties of rovibronic states associated with three different planar acetylene equilibrium configurations, namely trans bent acetylene, cis bent acetylene, and vinylidene (H 2C C). We make use of three different kinds of groups: (i) point groups, (ii) permutation-inversion (PI) groups, and (iii) extended PI groups. The PI group is G 4 or G 8, depending on whether C H bond breaking is impossible (no bent acetylene ↔ vinylidene interconversion) or possible. The extended PI groups are G 4 ( 2 ) and G 8 ( 2 ) , respectively, when the only large amplitude motions are the CCH bends at each end of the molecule, and G 4 ( 8 ) and G 8 ( 8 ) , respectively, when internal rotation is added as a third large amplitude motion. Applied to acetylene, the results indicate that there will be no splittings of the rovibronic levels unless CH bond breaking occurs. Even without bond breaking, however, states of the cis and trans isomers just below their interconversion barrier will show “staggerings” in their K-structures, i.e., a given vibrational level will have three tunneling components at slightly different energies: one component will have levels with K = 4 n only (where n is an integer), a second component will have levels with K = 4 n + 2 only, and the third will have only odd- K levels. New experimental results for the S 1–cis electronic state of acetylene [21] are reviewed, and are found to be consistent with the group theory in so far as comparison is possible.

Ab initio rovibronic states of the thioketenyl radical in its X2Π electronic ground state

We present an ab initio study of the thioketenyl (HCCS) radical in its degenerate X(2)Π electronic ground state. All rotational and vibrational degrees of freedom are taken into account including the electronic orbital and spin angular momenta. The structure of the rovibronic levels and the nature of the corresponding wave functions show resonances even at very low energies due to strong couplings between the bending, rotation, and spin terms in the Hamiltonian. Assignments from the dominant contributions of the eigenvectors are discussed in parallel with previously published data. The rotational structures for the first excited vibronic states are computed as well as transition intensities for the fundamental one.

A quantum defect model for the s, p, d, and f Rydberg series of CaF

We present an improved quantum defect theory model for the "s," "p," "d," and "f" Rydberg series of CaF. The model, which is the result of an exhaustive fit of high-resolution spectroscopic data, parameterizes the electronic structure of the ten ("s"Σ, "p"Σ, "p"Π, "d"Σ, "d"Π, "d"Δ, "f"Σ, "f"Π, "f"Δ, and "f"Φ) Rydberg series of CaF in terms of a set of twenty μ(ll('))(Λ) quantum defect matrix elements and their dependence on both internuclear separation and on the binding energy of the outer electron. Over 1000 rovibronic Rydberg levels belonging to 131 observed electronic states of CaF with n∗ ≥ 5 are included in the fit. The correctness and physical validity of the fit model are assured both by our intuition-guided combinatorial fit strategy and by comparison with R-matrix calculations based on a one-electron effective potential. The power of this quantum defect model lies in its ability to account for the rovibronic energy level structure and nearly all dynamical processes, including structure and dynamics outside of the range of the current observations. Its completeness places CaF at a level of spectroscopic characterization similar to NO and H(2).

Optical population of iodine molecule ion-pair states via valence states correlating with the third, I(2 P 1/2) + I(2 P 1/2), dissociation limit and their MI2 vdW complexes, M = I2, Xe

The first results of measurements and analysis of excitation spectra of the I2(D0 u + → X0 g + ) and I2(D0 u + → X0 g + and/or β1 g → A1 u ) luminescence, observed after three-step, λ1 + λ f + λ1, λ1 = 5508–5530 A, λ f = 10644.0 A, laser excitation of pure iodine vapour and I2 + Xe mixtures at room temperature via bound parts of the I2(0 g + , 1 u (bb)) valence states correlating with the third, I(2 P 1/2) + I(2 P 1/2), dissociation limit and their MI2 vdW complexes, M = I2, Xe, are presented. Luminescence spectra in the λlum = 2200–5000 A spectral range are also analyzed. Strong luminescence from the I2(D, γ, D′, and/or β) states is observed, though the two latter may be populated in optical transitions in a free iodine molecule if hyperfine coupling of the I2(0 g + and 1 u (bb)) state rovibronic levels occurs. We discuss possible mechanisms of optical population of the IP state.

Direct excitation of the “dark”b3Πstate predicted by deperturbation analysis of theA1Σ+−b3Πcomplex in KCs

The diode-laser-induced fluorescence spectra $b {}^{3}{\ensuremath{\Pi}}_{\ensuremath{\Omega}=0}^{+}\ensuremath{\rightarrow}{X}^{ 1}{\ensuremath{\Sigma}}^{+}$ originated from the rovibronic levels of the ``dark'' triplet $b {}^{3}{\ensuremath{\Pi}}_{\ensuremath{\Omega}=0}^{+}$ state of KCs dimers were recorded with a Fourier transform spectrometer with a resolution of 0.03 cm${}^{\ensuremath{-}1}$. Term values of 30 rovibronic levels $({v}_{b0}^{*}\ensuremath{\in}[14,18];{J}^{\ensuremath{'}}\ensuremath{\in}[47,134])$ below the minimum of perturbing $A {}^{1}{\ensuremath{\Sigma}}^{+}$ state were determined with 0.003--0.01 cm${}^{\ensuremath{-}1}$ uncertainty. The optimal excitation and detection lines for very weak spin-forbidden $b {}^{3}{\ensuremath{\Pi}}_{\ensuremath{\Omega}=0}^{+}\ensuremath{-}{X}^{ 1}{\ensuremath{\Sigma}}^{+}$ transitions have been properly predicted in the framework of the coupled-channels deperturbation analysis recently performed for the singlet-triplet $A {}^{1}{\ensuremath{\Sigma}}^{+}\ensuremath{-}b {}^{3}{\ensuremath{\Pi}}_{\ensuremath{\Omega}=0,1,2}^{+}$ complex [A. Kruzins et al., Phys. Rev. A 81, 042509 (2010)]. The lowest observed triplet level has only 8.6$%$ of singlet admixture.

ChemInform Abstract: Vibrationally Highly Excited Acetylene as Studied by Dispersed Fluorescence and Stimulated Emission Pumping Spectroscopy: Vibrational Assignment of the Feature States.

The dispersed fluorescence (DF) and stimulated emission pumping (SEP) spectra of acetylene originating from single rovibronic levels of the A 1Au state were measured with resolutions of 30 and 0.5 cm−1, respectively, in order to examine the vibrational level structure of the electronic ground X 1Σ+g state. The SEP spectra revealed that the number of vibrational levels under each peak in the DF spectra increases with vibrational energy from a single vibrational level below 8000 cm−1 to as many as ten vibrational levels above 16 500 cm−1. Taking account of the fact that a peak in the DF spectrum in the high energy region is composed of more than one level, a DF peak is called a feature state (or a feature). In the DF spectra from two trans‐bending levels (v3=2 and 3) of the A state a total of 140 DF features between 5 700 and 21 200 cm−1 were detected and long progressions in the trans bend (v‘4=6 –18) and CC stretch (v■2=0 –6) were identified.Below 14 000 cm−1, 26 out of the 50 observed features were un...

Enhanced sensitivity to the time variation of the fine-structure constant andmp/mein diatomic molecules: A closer examination of silicon monobromide

Recently it was pointed out that transition frequencies in certain diatomic molecules have an enhanced sensitivity to variations in the fine-structure constant $\ensuremath{\alpha}$ and the proton-to-electron mass ratio ${m}_{p}/{m}_{e}$ due to a near cancellation between the fine structure and vibrational interval in a ground electronic multiplet [V. V. Flambaum and M. G. Kozlov, Phys. Rev. Lett. 99, 150801 (2007)]. One such molecule possessing this favorable quality is silicon monobromide. Here we take a closer examination of SiBr as a candidate for detecting variations in $\ensuremath{\alpha}$ and ${m}_{p}/{m}_{e}$. We analyze the rovibronic spectrum by employing the most accurate experimental data available in the literature and perform ab initio calculations to determine the precise dependence of the spectrum on variations in $\ensuremath{\alpha}$. Furthermore, we calculate the natural linewidths of the rovibronic levels, which place a fundamental limit on the accuracy to which variations may be determined.

Rovibronically selected and resolved two-color laser photoionization and photoelectron study of nickel carbide cation

We have performed a two-color laser photoionization and photoelectron study of nickel carbide (NiC) and its cation (NiC(+)). By preparing NiC in a single rovibronic level of an intermediate vibronic state via visible laser excitation prior to ultraviolet laser photoionization, we have measured the photoionization efficiency spectrum of NiC near its ionization threshold, covering the formation of NiC(+)(X (2)Sigma(+);v(+)=0-3). We have also obtained well-resolved rotational transitions for the v(+)=0 and 1 vibrational bands of the NiC(+)(X (2)Sigma(+)) ground state. The assignment of rotational transitions observed between the neutral NiC intermediate state and the NiC(+) ion ground state has allowed the direct determination of a highly precise value for the ionization energy of NiC, IE(NiC)=67,525.1+/-0.5 cm(-1) (8.372 05+/-0.000 06 eV). This experiment also provides reliable values for the vibrational spacing [DeltaG(1/2)=859.5+/-0.5 cm(-1)], rotational constants (B(e)(+)=0.6395+/-0.0018 cm(-1) and alpha(e)(+)=0.0097+/-0.0009 cm(-1)), and equilibrium bond distance (r(e)(+)=1.628 A) for the NiC(+)(X (2)Sigma(+)) ground state. The experimental results presented here are valuable for benchmarking the development of more reliable ab initio quantum computation procedures for energetic and spectroscopic calculations of transition metal-containing molecules.

ChemInform Abstract: Electronic Spectroscopy and Structure of ClF

Optical-optical double resonance experiments have been used to identify and characterize five ion-pair states and several of the bound and repulsive valence states of ClF. This report provides a description of these experiments for and , and a summary of the current knowledge of the valence and ion-pair states. The important role of perturbations among the rovibronic levels of the bound valence states and their utilization in the double resonance technique is discussed. The ion-pair states of the same symmetry, = (E and f) and 1( and G) interact very strongly and the spectroscopy of these states is anomalous and, hence, interesting. Comparison is made to some recent ab initio calculations for ClF. One possible explanation of the irregular vibrational energy levels and rotational constants of the ion-pair states of and 1 symmetry is a crossing of the diabatic potentials of these states. Some currently unresolved questions about ClF spectroscopy are posed for future work. Where appropriate, analogy is made between the electronic states of ClF and the corresponding valence and ion-pair states of

An interpretation of the anomalous Π1 vibronic structure in the far-UV spectrum of CO

The far-UV spectrum of carbon monoxide presents numerous abnormal (1)Pi rovibronic levels in the region 92,000-105,000 cm(-1) which have been observed by several experimentalists. Yet, and in spite of various attribution attempts carried out over the past two decades, the nature of these levels is poorly understood and they still lack a definitive assignment. The absorption lines in this energy region are characterized by irregular energy level positions and spacings, and odd, smaller than expected, rotational constants. In the current contribution we address this puzzle by relying on recent ab initio calculations of several Rydberg and valence states of CO [G. J. Vazquez, J. M. Amero, H. P. Liebermann, and H. Lefebvre-Brion, J. Phys. Chem. A 113, 13395 (2009)], and on further new calculations in which we compute electronic transition moments between the ground state and several excited (1)Pi states. We focus on the perturbations between the adiabatic (1)Pi states, specifically on the interaction between the second and third potential energy curves, reported in our previous paper. The second adiabatic potential energy curve, which we refer to as E-E('), displays a distorted shape with two minima as a result of an avoided crossing with the third one. We report here the computation of the lowest vibronic levels of a system of two electronic states which undergo a strong Rydberg-valence interaction. Our vibronic calculations proceed as follows: from the second and third computed adiabatic curves we first obtain approximate diabatic curves for the (X (2)Sigma(+))3ppi E (1)Pi Rydberg state and for the valence E(') (1)Pi state. Then we solve a system of 2x2 coupled equations in order to obtain the perturbed vibronic energy levels and wave functions for the interacting E and E(') states. The computed vibronic levels obtained from the coupled equation treatment are compared to the first six observed (1)Pi levels. A good agreement is found with experiment for the four lowest vibronic levels and a reasonable accord for two higher levels.

Rotationally Resolved Ground State Vibrational Levels of HC2S Studied by Two-Color Resonant Four-Wave Mixing

A high-resolution study of the X(2)Pi(3/2) ground state rovibronic energy levels of jet-cooled HC(2)S radical using the double-resonance two-color four-wave mixing technique (TC-RFWM) is reported. The rotational structure of the bands is observed by excitation of selected R-branch lines in the origin band of the A(2)Pi(3/2)-X(2)Pi(3/2) electronic system. The second laser frequency is scanned to transfer the population from the rotational level(s) of the upper state to selected vibronic levels of the ground state. Fourteen rotationally resolved vibrational bands have been recorded for energies up to 1800 cm(-1) above the v'' = 0 X(2)Pi(3/2) electronic ground state. Effective rotational constants and origins are determined for levels that involve fundamental and overtone combinations of the nu(3) (CS stretch), nu(4) (CCH bend), and nu(5) (CCS bend) vibrations. This illustrates the power and advantages of the TC-RFWM approach for the study of the ground state manifold of reactive intermediates produced in low concentrations with high resolution, good signal-to-noise and wide dynamic range.

Resonant Coupling in the Heteronuclear Alkali Dimers for Direct Photoassociative Formation of X(0,0) Ultracold Molecules

Promising pathways for photoassociative formation of ultracold heteronuclear alkali metal dimers in their lowest rovibronic levels (denoted X(0,0)) are examined using high-quality ab initio calculations of potential energy curves currently available. A promising pathway for KRb, involving the resonant coupling of the 2(1)Pi and 1(1)Pi states just below the lowest excited asymptote (K(4s) + Rb(5p(1/2))), is found to occur also for RbCs and less promisingly for KCs also. The resonant coupling of the 3(1)Sigma(+) and 1(1)Pi states, also just below the lowest excited asymptote, is found to be promising for LiNa, LiK, and LiRb and less promising for LiCs and KCs. Direct photoassociation to the 1(1)Pi state near dissociation appears promising in the final dimers NaK, NaRb, and NaCs, although detuning more than 100 cm(-1) below the lowest excited asymptote may be required.