Vibrational Levels Of Ground State Research Articles

Simulation of the dispersed fluorescence spectrum of the NO[formula omitted][formula omitted] origin vibronic band

A vibronic Hamiltonian and transition dipole operator parametrized by high-level equation-of-motion coupled-cluster calculations are used as a basis for predicting the dispersed fluorescence spectrum of the B̃−X̃ origin band in the nitrate radical (NO3). The position and intensities of transitions to ground state vibrational levels observed in the photodetachment spectrum of the NO3 anion have previously been predicted to high fidelity with this Hamiltonian; it is expected that it also offers a basis for accurate prediction of the dispersed fluorescence spectrum. Comparison to experimental spectra provides considerable insight into various assignments. Significantly, this work joins a growing body of research that supports reassignment of the ground state ν3 vibrational fundamental to the region between 1050–1060 cm−1, which is more than 400 cm−1 below the feature to which it has traditionally been assigned. The in-plane vibrational levels below 2000 cm−1 are reviewed, with theory and experiment agreeing to within 25 cm−1 for all that have been observed experimentally. Finally, the various vibronic coupling mechanisms that affect the ground state energy levels of NO3 are summarized, and a discussion is provided about how the Lanczos algorithm can be used to efficiently calculate the dispersed fluorescence spectrum of the B̃−X̃ origin band.

Electronic Structures and Transition Properties of BeSe and BeTe Molecules.

The electronic structure of BeSe and BeTe molecules has been investigated using the ab initio CASSCF/(MRCI + Q) method at the spin-free and spin-orbit level. The potential energy curves, the permanent dipole moment, the spectroscopic constants Te, Re, ωe, and Be, and the dissociation energy De are determined in addition to the vertical transition energy Tv. The molecules’ percentages of ionic character are deduced, and the trends of the spectroscopic constants of the two molecules are compared and justified. A ro-vibrational study is performed using the canonical function approach to calculate the constants Ev, Bv, and Dv and the turning points Rmin and Rmax. All the ground-state vibrational levels have also been investigated. The radiative lifetimes of vibrational transitions among the electronic ground states are also discussed. The results for BeSe have been compared with the previously published data while those for BeTe molecules are presented here for the first time.

Analysis of the chemical network in a volume-production high-current negative hydrogen ion source

Complex simulations (e.g. multi-dimensional fluid models) usually prevent the use of very large chemistry models. In this work, the important physicochemical processes in a volume-production high-current negative hydrogen ion source (HCNHIS) are identified for a pressure range of 1–100 Torr using a global model. The particle species include H2(υ = 0–14), H(n = 1–3), , , H+, H−, and electrons. The simulation results indicate that for the production of negative hydrogen ions through dissociative attachments, the high vibrational levels of hydrogen molecules are important at low pressures, and the ground state and low vibrational levels of hydrogen molecules play an increasingly important role with increasing pressure. The reactions involving the ground state, low vibrational levels, and neighboring levels of each level tend to dominate the production of vibrational levels and transitions between them in the volume-production HCNHIS. With increasing pressure, the electron energy dissipation shifts from dissociation of H2(υ = 0) and electron excitation of H2(υ = 0) through an indirect mechanism followed by radiative decay (the EV process) to electron excitation of H2(υ = 0) through a resonant mechanism (the eV process). A valuable subset of reactions provided by the simplified model is proposed in the investigated pressure range, which could be incorporated in more complex simulations. The results obtained with the simplified model under different simulation conditions are within an acceptable error margin of the results for the full model, which indicates that the robustness of the simplified model of chemical reactions is guaranteed to some extent.

Predissociation and pressure dependence in the low frequency far wing of the Wulf absorption band of ozone near 1.2 µm

The weak low frequency tail of the ozone Wulf band is newly studied by high sensitivity cavity ring down spectroscopy (CRDS) in the 7920–8700 cm−1 range. Although strongly obscured by impurity lines, the ozone absorption signature shows up in the recorded spectra as two mostly unresolved absorption bands. These two bands with maximum near 8154 and 8450 cm−1 are hot bands from the (020) and (100) ground state vibrational levels reaching the same predissociated 3A2(000) upper state of 16O3. The observed bands include a mostly structureless continuum and lines exhibiting a clear broadening due to the predissociation of the 3A2(000) upper state. On the basis of assignments of the rotational structure available in the literature for the 3A2(000)-X1A1(000) cold band centered near 9553 cm−1, seventy-four relatively narrow lines could be rotationally assigned to the 3A2(000)-X1A1(020) and 3A2(000)-X1A1(100) hot bands. A line shape analysis, performed using a Voigt profile, provided the width of the Lorentzian component. Additional recordings performed at various pressures for 18 lines allowed to disentangle the pressure and predissociation contributions to the fitted Lorentzian widths. As a result, the newly derived pressure broadening coefficients of the considered rovibronic transitions are found to be similar to those of the rovibrational infrared bands. All the lines studied are affected by significant predissociation due the spin-orbit coupling between the 3A2(000) level and high lying dissociative vibrational levels of the X1A1 electronic ground state. The resulting set of predissociation widths for sixty lines ranges between 9 × 10−3 and 0.2 cm−1 corresponding to upper state lifetime of 560 and 25 ps, respectively. The reported results are discussed in relation with previous experimental and theoretical studies.

Accuracy of Morse and Morse-like oscillators for diatomic molecular interaction: A comparative study

This study aims at comprehensively evaluating and comparing the goodness-of-fit of several potential energy curves (PECs), which are Morse, Manning-Rosen, Rosen-Morse and Modified-Rosen-Morse oscillators, to the corresponding experimental Rydberg-Klein-Rees (RKR) or RKR-style data of diatomic molecules. In this work, we also determined vibrational energies of the diatomics based on Bohr-Sommerfeld quantization rule. The goodness-of-fit to RKR data of 34 electronic states of 17 diatomics and the accuracy of the calculated vibrational energies were compared for the four oscillators and reported simultaneously for the first time in this study. These results showed that some oscillators demonstrated better goodness-of-fit than the others. Overall, the (Modified)-Rosen-Morse oscillators generated more accurate vibrational levels for most molecules studied, while Manning-Rosen oscillator was generally better for molecules in their excited electronic states. Although all oscillators performed well for more classical molecules, the Morse oscillator was superior to the other three in describing the ground states of 12C16O and 28Si32S. Particularly, it reproduced all 38 observed experimental ground state vibrational levels of 12C16O with error below 0.79% and even accurately predicted four states unobserved experimentally.

Theoretical study of MgNa+ ionic system: potential energy curve, vibrational levels, dipole moments, radiative lifetimes and laser-cooling analysis

An extensive ab-initio quantum chemistry study and a discussion of the possible laser cooling and formation of the heteronuclear ionic MgNa+ molecule is presented in this paper. Our work is based on the use of non–empirical pseudo-potentials for the Mg2+ and Na+ cores, large Gaussian basis sets, parametrized l–dependent polarization potentials, and full valence configuration interaction calculations. We present here adiabatic potential energy curves of the ground and 44 low-lying excited electronic states of 1,3Σ+, 1,3Π, 1,3Δ symmetries, and their spectroscopic parameters (Re, De, Te, ωe, ωexe, and Be). Furthermore, numerous ionic – neutral avoided crossings, specially between higher adjacent electronic states of 1,3Σ+, 1,3Π symmetries, are identified and interpreted. The energy separations between these avoided crossings are also calculated. The electric dipole moment curves have been computed for a wide range of inter-nuclear distances. The vibrational energies are obtained by solving the nuclear Schrodinger equation, using the calculated potential energy curves. Thereafter, spontaneous and black-body radiation induced transition rates are calculated to obtain the ground and excited states vibrational level lifetimes. It has been observed that the lifetimes of the ground state vibrational levels are of the order of a second, while those of the excited states, mainly the 21Σ+ state, have the order of a nanosecond.

High sensitive label-free optical sensor based on Goos\u2013H\xe4nchen effect by the single chirped laser pulse

We consider a four-level molecular system with two ground-state vibrational levels and two excited-state vibrational levels inside a constant cavity configuration. We discuss the reflected and transmitted Goos–Hänchen (GH) shifts of a positive and negative single-chirped laser pulse. The impacts of the laser field detuning, intensity of applied laser field, and appropriately tuning the chirp rate on GH shifts are then analyzed. It is also found that this sensor is very sensitive to the refractive index of the intracavity medium, which can coherently be controlled by the medium parameters. The results show that such a sensor can be most effective for detecting biological molecules with low concentration than the large number density, where a bit variation in the concentration of sample will lead to a great variation on the GH shifts.

Ro-vibrational cooling of diatomic molecules Cd2 and Yb2: rotational energy structure included

Method of ro-vibrational cooling of Cd and Yb molecules occupying initially their excited ro-vibrational levels in the ground electronic state is proposed. The method employs the and electronic transitions in Cd and Yb, respectively. The cooling relies on a successive decrease of population of the ground-state vibrational and rotational levels using a series of laser-induced excitations from a selected ground-state (, ) to the excited-state (, ) ro-vibrational levels, followed by spontaneous de-excitations to the ground state. The proposal is an extension of the vibrational cooling method recently proposed by Urbańczyk et al. [Mol. Phys. 116, 3475–3486 (2018)].

NO3 full-dimensional potential energy surfaces and ground state vibrational levels revisited

A new full-dimensional (6D) diabatic potential energy surface (PES) model is presented representing the five lowest PESs corresponding to the X̃2A2′,Ã2E″, and B̃2E′ electronic states of the nitrate radical (NO3). It is based on high-level ab initio calculations of roughly 90000 energy data over a wide range of nuclear configurations and represents the energies with a root mean-squares (rms) error of about 100 cm−1. An accurate dipole surface was developed for the X̃ state as well. The new PES model is used to re-investigate the infra-red (IR) spectrum corresponding to the electronic ground state by full dimensional quantum dynamics simulations. Vibrational eigenstates, IR transition probabilities, and isotopic shifts are computed and analyzed. Levels up to 2000 cm−1 are obtained and show good to excellent agreement with known experimental values. Some larger deviations are observed and discussed as well. The new results are in agreement with previous theoretical studies that the disputed ν3 fundamental corresponds to a frequency of roughly 1022 cm−1 and that the prominent experimental feature observed at 1492 cm−1 is due to the 3141 (e′) combination mode. Observed discrepancies in the IR intensities may be explained by coupling to the B̃ state which is also analysed by diabatic decomposition of the eigenstates.

Spectroscopic and theoretical studies of ThCl and ThCl.

The electronic structures of ThCl and ThCl+ have been examined using laser induced fluorescence and two-photon ionization techniques. Rotationally resolved spectra, combined with the predictions from relativistic electronic structure calculations, show that the ground state of the neutral molecule is Th+(7s26d)Cl-, X2Δ3/2. Dispersed fluorescence spectra for ThCl revealed the ground state vibrational levels v = 0-10 and low energy electronic states that also originate from the atomic ion 7s26d configuration. Pulsed field ionization-zero kinetic energy photoelectron spectroscopy established an ionization energy (IE) for ThCl of 51 344(5) cm-1, and the ThCl+ vibrational term energies of the v = 1-3 levels. The zero-point level of the first electronically excited state was found at 949(2) cm-1. Comparisons with high-level theoretical results indicate that the ground and excited states are Th2+(7s6d)Cl- X3Δ1 and Th2+(7s2)Cl- Σ+1, respectively. Relativistic coupled cluster composite thermochemistry calculations yielded an IE within 1.2 kcal/mol of experiment and a bond dissociation energy (118.3 kcal/mol) in perfect agreement with previous experiments.

Microwave Spectra, Structure, and Ring-Puckering Vibration of Octafluorocyclopentene.

The rotational spectra of octafluorocyclopentene (C5F8) has been measured for the first time using pulsed jet Fourier transform microwave spectroscopy in a frequency range of 6 to 16 GHz. As in the molecule cyclopentene, the carbon ring is nonplanar, and inversion through the plane results in an inversion pair of ground state vibrational energy levels with an inversion splitting of 18.4 MHz. This large amplitude motion leads to the vibration-rotation coupling of energy levels. The symmetric double minimum ring-puckering potential function was calculated, resulting in a barrier of 222 cm-1. The rotational constants A0 = 962.9590(1) MHz, B0 = 885.1643(4) MHz, C0 = 616.9523(4) MHz, A1 = 962.9590(1) MHz, B1 = 885.1643(4) MHz, C1 = 616.9528(4) MHz, and two centrifugal distortion constants for each state were determined for the parent species and all 13C isotopologues. A mixed coordinate molecular structure was determined from a least-squares fit of the ground state rotational constants of the parent and each 13C isotopologue combined with the equilibrium bond lengths and angles from quantum chemical calculations.

High-resolution room temperature and jet-cooled spectroscopic investigation of 15NH3 in the ν1+ν3 band region (1.51 μm)

Spectra of 99% isotopically pure 15NH3 were recorded using cavity ring-down (CRD, 6567−6639cm−1) and Fourier transform (FT, 6350–6985cm−1) spectroscopy under jet cooled and room temperature conditions, respectively. Measured line positions on both data sets improve on literature values, in particular by one order of magnitude for the ν1+ν3 band. A room temperature list of line positions, with approximate line intensities, is provided, much more complete and precise than presently available. Line broadening effects in the CRD spectrum allowed lines with J′′′- values between 0 and 3 to be identified. Ground state combination differences were used to refine the assignments, further assisted by intensity ratios between the two data sets. Reliable values for J, K and inversion symmetry of the ground state vibrational levels, as well as further information on a/s doublets could be obtained, updating and extending literature assignments.

Hindered rotor tunneling splittings: an application of the two-dimensional non-separable method to benzyl alcohol and two of its fluorine derivatives.

In this work we present a novel application of the two-dimensional non-separable (2D-NS) method to the calculation of torsional tunneling splittings in systems with two hindered internal rotors. This method could be considered an extension of one-dimensional methods for the case of compounds with two tops. The 2D-NS method includes coupling between torsions in the kinetic and potential energy. Specifically, it has been applied to benzyl alcohol (BA) and two of its fluorine derivatives: 3-fluorobenzyl alcohol (3FBA) and 4-fluorobenzyl alcohol (4FBA). These molecules present two torsions, i.e., about the -CH2OH (ϕ1) and -OH (ϕ2) groups. The electronic structure calculations to build the two-dimensional torsional potential energy surface were performed at the DF-LMP2-F12//DF-LMP2/cc-pVQZ level of theory. For BA and 4FBA the calculated ground-state vibrational level splittings are 429 and 453 MHz, respectively, in good agreement with the experimental values of 337.10 and 492.82 MHz, respectively. In these two cases there are four equivalent wells and the tunneling splitting is the result of transitions between the two closer minima along ϕ1. The analysis of the wavefunctions, as well as the previous experimental work on the system, supports this conclusion. For 3FBA the observed ground-state splitting is 0.82 MHz, whereas in this case the calculated value amounts only to 0.02 MHz. The 2D-NS method, through the analysis of the wavefunctions, shows that this tiny tunneling splitting occurs between the two most stable minima of the potential energy surface. Additionally, we predict that the first vibrationally excited tunneling splitting will also be small and exclusively due to the interconversion between the second lowest minima.

An experimental and theoretical study of the electronic spectrum of the HBCl free radical.

Following our previous discovery of the spectra of the HBX (X = F, Cl, and Br) free radicals [S.-G. He, F. X. Sunahori, and D. J. Clouthier, J. Am. Chem. Soc. 127, 10814 (2005)], the Ã(2)A(″)Π-X̃(2)A(') band systems of the HBCl and DBCl free radicals have been studied in detail. The radicals have been prepared in a pulsed electric discharge jet using a precursor mixture of BCl3 and H2 or D2 in high pressure argon. Laser-induced fluorescence (LIF) and single vibronic level emission spectra have been recorded to map out the ground and excited state vibrational energy levels. The band system involves a linear-bent transition between the two Renner-Teller components of what would be a (2)Π electronic state at linearity. We have used high level ab initio theory to calculate the ground and excited state potential energy surfaces and have determined the vibronic energy levels variationally. The theory results were used to assign the LIF spectra which involve transitions from the ground state zero-point level to high vibrational levels of the excited state. The correspondence between theory and experiment, including the transition frequencies, upper state band symmetries, and H, B, and Cl isotope shifts, was used to validate the assignments.

Low-temperature high-resolution absorption spectrum of 14NH3 in the ν1+ν3 band region (1.51 μm)

Jet-cooled spectra of 14NH3 and 15NH3 in natural abundance were recorded using cavity ring-down (CRDS, 6584–6670 cm−1) and cavity enhanced absorption (CEAS, 6530–6700 cm−1) spectroscopy. Line broadening effects in the CRDS spectrum allowed lines with J″-values between 0 and 3 to be identified. Intensity ratios in 14NH3 between the jet-cooled CRDS and literature room-temperature data from Sung et al. (J. Quant. Spectrosc. Radiat. Transfer, 113 (2012), 1066) further assisted the line assignments. Ground state combination differences were extensively used to support the assignments, providing reliable values for J, K and inversion symmetry of the ground state vibrational levels. CEAS data helped in this respect for the lowest J lines, some of which are saturated in the CRDS spectrum. Further information on a/s doublets arose from the observed spectral structures. Thirty-two transitions of 14NH3 were assigned in this way and a limited but significant number (19) of changes in the assignments results, compared to Sung et al. or to Cacciani et al. (J. Quant. Spectrosc. Radiat. Transfer, 113 (2012), 1084). Sixteen known and 25 new low-J transitions were identified for 15NH3 in the CRDS spectrum but the much scarcer literature information did not allow for any more refined assignment. The present line position measurements improve on literature values published for 15NH3 and on some line positions for 14NH3.

Vibrations of porphycene in the S and S1 electronic states: Single vibronic level dispersed fluorescence study in a supersonic jet

Supersonic jet-isolated porphycene has been studied using the techniques of laser-induced fluorescence excitation, single vibronic level fluorescence, and spectral hole burning, combined with quantum mechanical calculations of geometry and vibrational structure of the ground and lowest electronically excited singlet states. Porphycene is a model for coherent double hydrogen tunneling in a symmetrical double well potential, as evidenced by tunneling splittings observed in electronic absorption and emission. The results led to reliable assignment of low frequency modes in S0 and S1 electronic states. The values of tunneling splitting were determined for ground state vibrational levels. In the case of tautomerization-promoting 2A(g) mode, tunneling splitting values significantly increase with the vibrational quantum number. Mode coupling was demonstrated by different values of tunneling splitting obtained for coexcitation of two or more vibrations. Finally, alternation of relative intensity patterns for the components of 2A(g) tunneling doublet observed for excitation and emission into different vibrational levels suggests that the energy order of levels corresponding to (+) and (-) combinations of nuclear wave functions is different for even and odd vibrational quantum numbers.

Proton dynamics at low and high temperatures in a novel ferroelectric diammonium hypodiphosphate (NH4)2H2P2O6 (ADhP) as studied by 1H spin–lattice relaxation time and second moment of NMR line

Proton spin–lattice relaxation times T1 at 24.7MHz and 15MHz and second moment of NMR line have been applied to study molecular dynamics of a novel ferroelectric (NH4)2H2P2O6 (Tc=178K) in the temperature range 10–290K. Low-temperature T1 behaviour below Tc is interpreted in terms of Haupt’s theory and Schrödinger correlation time of tunnelling jumps. A shallow T1 minimum observed around 39K is attributed to the C3 classical motion of “intra” proton–proton vectors of NH3 (ammonium groups NH4+ may perform stochastic jumps about any of the four C3 symmetry axes). The tunnelling splitting of the ground state vibrational level, (νT)v0, of the same frequency for both ammonium groups was estimated as high as 900MHz ((ℏωT)v0=3.7μeV). This tunnelling splitting exists only in the ferroelectric phase. Magnetisation recovery is found to be non-exponential in the temperature regime 63–48K. The temperature of 63K is the discovered Ttun above which the probability of stochastic tunnelling jumps equals zero. The T1 relaxation time is temperature independent below 25K, which is related to a constant value of the correlation time characterising tunnelling jumps according to Schrödinger. The T1 minima observed in the paraelectric phase (204K at 15MHz and 213K at 24.7MHz) as well as second moment reduction at about 130K are attributed to isotropic motion of all protons.

Electronic Spectra and Reversible Photoisomerization of Protonated Naphthalenes in Solid Neon

Alpha- and beta-protonated naphthalenes (α- and β-HN(+)) were investigated by electronic absorption and fluorescence spectroscopies in 6 K neon matrixes using a mass-selected C(10)H(9)(+) ion beam. The absorption spectra reveal S(1)/S(2) ← S(0) transitions with onsets at 502.1 and 396.1 nm for α-HN(+), and 534.5 and 322.3 nm in the case of β-HN(+). Wavelength-dispersed fluorescence was detected for α-HN(+), starting at 504.4 nm. Light-induced α-HN(+) → β-HN(+) isomerization was observed upon S(2) ← S(0) excitation of α-HN(+), whereas β-HN(+) relaxed back into the more stable alpha form either upon excitation to S(1) or via thermal population of the ground state vibrational levels near the top of the energy barrier between the two isomers. The intramolecular proton transfer leading to the α-HN(+) ↔ β-HN(+) photoisomerization is fully reversible. The observations are explained with the support of theoretical calculations on the ground- and excited states of the isomers, vertical excitation and adiabatic energies, minimum-energy pathways along the relevant reaction coordinates, and conical intersections between the electronic states.

Electron-impact resonant vibration excitation cross sections and rate coefficients for carbon monoxide

Resonant vibrational and rotation–vibration excitation cross sections for electron–CO scattering are calculated in the 0–10 eV energy range for all 81 vibrational states of CO, assuming that the excitation occurs via the 2Π shape resonance. Static exchange plus polarization calculations performed using the R-matrix method are used to estimate resonance positions and widths as functions of internuclear separation. The effects of nuclear motion are considered using a local-complex-potential model. Good agreement is obtained with available experimental data on excitation from the vibrational ground state. Excitation rates and cross sections are provided as a function of the initial CO vibrational state for all ground state vibrational levels.

Fourier transform emission spectroscopy of the A2Π–X2Σ+ (red) system of 13C14N (II)

High resolution emission spectra of the A2Π–X2Σ+ transition of 13C14N have been measured in the 15000–24000cm−1 region. Molecules were produced by the reaction of 13CH4 and 14N2 in an active nitrogen afterglow discharge. The spectra were recorded using the Fourier transform spectrometer associated with the McMath-Pierce Solar Telescope of the National Solar Observatory. A rotational analysis of 27 bands involving the excited state vibrational levels v′=9–22 and the ground state vibrational levels up to v″=12 has been obtained. An improved set of spectroscopic constants has been determined for the v=0–22 levels of the A2Π state by combining the present measurements with those reported previously for the v=0–8 vibrational levels of the A2Π state [Ram et al., Astrophys. J. Suppl. Ser. 188 (2010) 500] and existing infrared and millimeter-wave measurements of 13C14N. The 6–3, 7–4, 8–5 and 9–6 bands of the B2Σ+–A2Π transition were also identified in the 23300–24000cm−1 region and were included in the final analysis. An experimental line list and calculated term values are provided.