High-lying Vibrational Levels Research Articles

Accurate ground state potential of Cu2 up to the dissociation limit by perturbation assisted double-resonant four-wave mixing.

Perturbation facilitated double-resonant four-wave mixing is applied to access high-lying vibrational levels of the X 1Σg + (0g +) ground state of Cu2. Rotationally resolved transitions up to v″ = 102 are measured. The highest observed level is at 98% of the dissociation energy. The range and accuracy of previous measurements are significantly extended. By applying the near dissociation equation developed by Le Roy [R. J. Le Roy, J. Quant. Spectrosc. Radiat. Transfer 186, 197 (2017)], a dissociation energy of De = 16 270(7) hc cm-1 is determined, and an accurate potential energy function for the X 1Σg + (0g +) ground state is obtained. Molecular constants are determined from the measured transitions and by solving the radial Schrödinger equation using this function and are compared with results from earlier measurements. In addition, benchmark multi-reference configuration interaction computations are performed using the Douglas-Kroll-Hess Hamiltonian and the appropriate basis of augmented valence quadruple ζ type. Coupled-cluster single, double, and perturbative triple calculations were performed for comparison.

Photodissociation spectroscopy of N2O+ in the ion storage ring RICE.

The A2Σ+-X2Π electronic transition of the nitrous oxide cation, N2O+, was measured via photodissociation spectroscopy in a cryogenic electrostatic ion storage ring. Rotationally resolved spectra of the N-O stretching vibrational sequence were obtained by detecting neutral N fragments produced via N2O+ → NO+ + N predissociation channels. A new set of molecular constants was determined for the high-lying vibrational levels of the A2Σ+ state.

Quantum dynamics of a millikelvin quasibound KRb complex in a low-frequency field

We investigate computationally the quantum dynamics of a metastable $^{40}\mathrm{K}^{\phantom{\rule{0.16em}{0ex}}87}\mathrm{Rb}$ complex in the ground electronic state ($X{\phantom{\rule{0.16em}{0ex}}}^{1}{\mathrm{\ensuremath{\Sigma}}}^{+}$) under an intense continuous-wave low-frequency field. We focus on an initial condition where the atoms are quasibound in an orbiting resonance with an energy that corresponds to a kinetic temperature of 62 mK and with a lifetime of 3 ns. A microwave field is tuned either to another lower-lying orbiting resonance or to a high-lying bound vibrational level. In both cases, we observe a transient photoacceleration of the half-collision. However, the photodissociation of the complex is suppressed by strong quasibound-free Rabi oscillations, although it still dissociates nonradiatively with the lifetime of the initial orbiting resonance. During the transient period, a sizable multiphoton association in high-lying vibrational levels is achieved, accompanied by a development of a wide rotational distribution. Therefore, this mechanism seems promising as the basis of a general strategy for the controlled formation of diatomic molecules from gases at millikelvin temperatures.

IVR Dynamics of Vibrational Levels of the ν1 Mode in (CF3)2C═C═O Molecules Excited by Resonant IR Femtosecond Radiation.

The intramolecular dynamics of vibrational levels (up to v = 5) of the ν1 mode in the (CF3)2CCO molecule that is induced by a multiphoton selective excitation of this mode by resonant femtosecond IR radiation has been studied. The times of intramolecular vibrational energy redistribution (IVR) from each vibrational level to remaining molecular modes have been determined. In accordance with theoretical predictions, a decrease in the IVR time with increasing quantum number v has been observed for the first time. A sharp decrease in the IVR time (down to 1.5 ps) at a wavelength of 2129 cm-1, corresponding to the v = 3 → v = 4 vibrational transition, is revealed. It has been shown that, with a negative chirp of a femtosecond radiation pulse, the population of high-lying vibrational levels of the ν1 mode increases significantly.

High-temperature partition functions, specific heats and spectral radiative properties of diatomic molecules with an improved calculation of energy levels

The level energies of diatomic molecules calculated by the frequently used Dunham expansion will become less accurate for high-lying vibrational and rotational levels. In this paper, the potential curves for the lower-lying electronic states with accurate spectroscopic constants are reconstructed using the Rydberg–Klein–Rees (RKR) method, which are extrapolated to the dissociation limits by fitting of the theoretical potentials, and the rest of the potential curves are obtained from the ab-initio results in the literature. Solving the rotational dependence of the radial Schrödinger equation over the obtained potential curves, we determine the rovibrational level energies, which are then used to calculate the equilibrium and non-equilibrium thermodynamic properties of N2, N2+, NO, O2, CN, C2, CO and CO+. The partition functions and the specific heats are systematically validated by available data in the literature. Finally, we calculate the radiative source strengths of diatomic molecules in thermodynamic equilibrium, which agree well with the available values in the literature. The spectral radiative intensities for some diatomic molecules in thermodynamic non-equilibrium are calculated and validated by available experimental data.

Intramolecular vibrational dynamics of ν1mode in (CF3)2C=C=O molecule induced by resonant IR femtosecond radiation

Intramolecular dynamics of the vibrational levels (up to v = 5) of the ν 1 mode in (CF 3 ) 2 CCO molecule, induced via multiphoton selective excitation of this mode by resonant femtosecond IR radiation, was studied. The times of intramolecular vibrational energy redistribution ( IVR ) of each vibrational level v to the remaining modes of the molecule were measured. In accordance with the theory predictions the decrease of IVR time with increasing v is observed. A sharp reduction of the IVR time (up to 1 ps) at a wavelength of 2130 cm −1 of transition v=3 → v=4 was found. It was shown that with a negative chirp of a femtosecond radiation pulse the population of high-lying vibrational levels of ν 1 modes significantly increases.

Vibrational and electronic collisional-radiative model in air for Earth entry problems

The two-temperature collisional-radiative model CoRaM-AIR, working over a wide range for pressure and temperatures, has been developed for the flow conditions around a space vehicle entering the Earth's atmosphere. The species N2, O2, NO, N, O, Ar, N2+, O2+, NO+, N+, O+, Ar+, and free electrons are taken into account. The model is vibrationally specific on the ground electronic state of N2, O2, and NO, and electronically specific for all species, with a total of 169 vibrational states and 829 electronic states, respectively. A wide set of elementary processes is considered under electron and heavy particle impact given the temperatures involved (up to 30 000 K). This set corresponds to almost 700 000 forward and backward elementary processes. The relaxation from initial thermal or chemical nonequilibrium is studied for dissociation-ionization situations in conditions related to the FIRE II flight experiment. Boltzmann plots clearly prove that the vibrational and electronic excitation distributions are far from being Boltzmanian. In particular, high-lying vibrational levels remain underpopulated for most of the duration of the relaxation. This relaxation can be separated in a first phase characterized by the dissociation and the excitation of the molecular species, and a second phase leading to the excitation and the ionization of the dissociation products. Owing to the vibrational relaxation, the time scales are slightly higher than the ones predicted by former kinetic mechanisms usually used in flow simulations. In the present FIRE II conditions, radiation does not play a significant role.

Experimental Determination of the Rotational Constants of High-Lying Vibrational Levels of Ultracold Cs2 in the 0g– Purely Long-Range State

We report on a quantitative experimental determination of the rotational constants for the high-lying vibrational levels of the ultracold pure long-range Cesium molecules formed via photoassociation. The scheme relies on a precise reference of frequency difference in a double photoassociation spectroscopy, which is induced by two laser beams based on an acoustic-optical modulator. The rotational constants are obtained by fitting a nonrigid rotor model into the frequency intervals of the neighboring rotational levels deduced from the reference.

High Sensitivity Measurement and Accurate Analysis of the Vibrational Spectroscopy Near the (6S1/2+6P3/2) Dissociation limit for 1g State of Cs2

The photoassociation spectroscopic data of the long-range molecular 1g state of Cs 2 in the asymptotic range red detuned [-5.02, -2.45 cm -1 ] to the (6S 1/2 +6P 3/2 ) dissociation limit detected using photon counting technique are presented and 18 new high-lying vibrational energy levels are obtained. Fitting experimental data to the improved LeRoy–Bernstein (LRB) formula, we have obtained the long-range molecular coefficient c 3 with a high precision and also demonstrated the necessity of the improved LRB formula for more precise c 3 coefficient by analyzing the residual from fitting procedure.

Direct Measurement of the Cs2 0u+ (P3/2) High-Lying Vibrational Spectroscopy Using Photon Counting

We report on the photoassociation of cold Cs atoms giving spectroscopy data of the 0 u + long-range molecular state in the asymptotic range of [-6.2, -2.5 cm -1 ] close to the 6S 1/2 +6P 3/2 dissociation limit using photon counting technique. 24 new high-lying vibrational levels of the 0 u + long-range state are identified to lead to the formation of excited molecules in the photoassociation process. Fitting experimental data to improved LeRoy–Bernstein formula, we obtain long-range molecular coefficient with a high precision.

Inelastic Collisions of Ultracold Heteronuclear Molecules in an Optical Trap

Ultracold RbCs molecules in high-lying vibrational levels of the a3Sigma+ ground electronic state are confined in an optical trap. Inelastic collision rates of these molecules with both Rb and Cs atoms are determined for individual vibrational levels, across an order of magnitude of binding energies. The long-range dispersion coefficients for the collision process are calculated and used in a model that accurately reproduce the observed scattering rates.

Photoassociation of ultracold K atoms: Observation of high lying levels of the 1g∼1 1Πg molecular state of K2

Very high-lying vibrational levels of the 1g∼1 1Πg electronic state of K2 have been observed in a photoassociation experiment using an ion detection scheme. The photoassociation measurements have been treated together with laser induced fluorescence data recorded by Fourier transform spectrometry to construct a pointwise potential curve for this electronic state. Several vibrational levels were observed by both techniques, so the dissocation energy can be deduced without extrapolation, from the sum of binding energies measured in photoassociation and vibrational energies established with respect to the potential minimum (defined by the fluorescence data), giving De=1290.292±0.002 cm−1 (1 standard deviation). The potential curve reproduces over 2000 term values (up to v=138) with a root mean square error of 0.0025 cm−1. Nevertheless, small differences are found between the rotational constants generated from the potential curve and the effective rotational constants deduced from binding energy measurements at very high v. The smoothness of the outermost part of the pointwise potential energy curve has been investigated through fits to a Hund’s case (c) asymptotic model.

A master equation study of vibration-dissociation coupling in shock-heated oxygen molecules

The vibration-dissociation coupling phenomena in shock-heated oxygen molecules highly dilute in an argon heat-bath have been studied numerically. State-to-state transition rate coefficients were evaluated by using relatively simple models developed through the information theoretical approach. The master equation was solved by numerical integration to obtain time-resolved vibrational population distributions. The results of the master equation analysis are compared with those obtained by using a widely-used phenomenological vibration-dissociation coupling model. The results show that during the relaxation process the depletion of high-lying vibrational energy levels is severe and significantly affects bulk properties related to dissociation and that the phenomenological model can reproduce qualitatively the bulk relaxation process found in the master equation analysis.

Calculated rates for the electron impact dissociation of molecular hydrogen: mixed isotopomers and scaling laws

Following our calculations of electron impact dissociation rates of molecular H2, D2 and T2 (Trevisan and Tennyson 2002 Plasma Phys. Control. Fusion 44 1263–76), calculations for the mixed isotopomers HD, HT and DT have been made. Total cross sections and energy differential cross sections at threshold energies as a function of vibrational states (v) for HD: v = 0–5, for HT: v = 0–5 and for DT: v = 0–7 are calculated for the electron impact dissociation through excitation to the b 3Σu+ excited electronic state, which is the dominant dissociation process at such energies. The rates of dissociation as a function of electron temperature for each state are parametrized. Coinciding with our previous results, near-threshold rates are shown to be so critically dependent on the vibrational level that dissociation from very high-lying vibrational levels must be included in calculations of the rate at local thermal equilibrium (LTE) even at low temperature. Rates for the higher vibrational levels are obtained by extrapolation following the procedure discussed in our previous publication, and are then used to calculate the LTE rate. The LTE rate is an order of magnitude greater than the v = 0 rate. A scaling law for the electron impact dissociation cross sections of vibrationally excited H2 and its isotopomers has been derived.

Calculated rates for the electron impact dissociation of molecular hydrogen, deuterium and tritium

At temperatures below 15 000 K, the major pathway for the electron impact dissociation of H2 is through excitation to the b 3Σu+ excited electronic state. Total cross sections and energy differential cross sections for threshold energies as a function of vibrational states (v) for H2 v = 0–4, D2 v = 0–6 and T2 v = 0–7 are calculated. The rates of dissociation as a function of electron temperature for each state are parametrized. Near-threshold rates are shown to be so critically dependent on the vibrational level that dissociation from very high-lying vibrational levels must be included in calculations of the rate at local thermal equilibrium (LTE) even at low temperature. An adapted version of the extrapolation procedure of Stibbe and Tennyson (1999 Astrophys. J. 513 L147) is used to approximate the rates for all of the higher vibrational levels, which are then used to calculate the LTE rate. The LTE rate is an order of magnitude greater than the v = 0 rate. Calculations of energy differential cross sections suggest that impact dissociation of vibrationally excited molecules could be the source of low energy H atoms observed in tokamak plasmas.

3312 再突入カプセル周りの極超音速流れにおける熱化学的緩和現象

We report a numerical study of vibration-dissociation coupling which is one of the most important thermochemical relaxation phenomena in hypersonic flows around a reentry capsule. A full set of vibrational master equations was numerically solved to obtain time-resolved population distribution of the vibrational states as well as bulk properties during the relaxation process. State-resolved rate coefficients were determined using the information theoretical approach. Our results show that a quasi-steady state (QSS) exists during the relaxation process, and that the bulk dissociation mostly proceeds during the QSS. It is also shown that the high-lying vibrational energy levels are depleted during the QSS and that the severe depletion of high-lying levels strongly affects the average dissociation rate coefficient and the average vibrational energy loss due to dissociation.

The role played by electronic correlation of target on the vibrational excitation cross sections of H2 by electron impact

We report a systematic study on the role played by electronic correlation of target on vibrational excitation processes of molecules by electron impact. More specifically, cross sections for vibrationally elastic and inelastic electron–H2 collisions are reported in the 1.5–40eV range. In our study, the electron–molecule interaction potential is derived using both the near-Hartree–Fock and the configuration interaction target wavefunctions. The body-frame vibrational close-coupling equations are solved using the method of continued fractions (MCF). Our study has shown that the MCF is a very efficient method for solving such scattering equations. In addition, the calculated results have shown that the electronic correlation effects of target significantly influence the calculated vibrational excitation cross sections at low incident energies and for the excitations leading to high-lying vibrational levels. Nevertheless, these effects are not relevant at higher incident energies.

The High-Lying Vibrational Levels and Dissociation Energy of the a3Σ+u State of 7Li2

Perturbation-facilitated optical–optical double resonance (PFOODR) has been used to access the 23Πg state of 7Li2 via the excitation scheme using two single-mode tunable lasers. The selected () mixed level provides a gateway through which the triplet manifold can be accessed. Fluorescence from single rovibrational levels of 23Πg to the state was detected at high resolution using a Fourier transform spectrometer. Transitions to v = 0–9 in the state were observed, covering the potential well almost to the dissociation limit. The data were analyzed using a near dissociation expansion (NDE) technique and the resulting vibrational and rotational parameters were used to calculate a new RKR potential curve which reproduced the observed energy levels to within a rms error of 0.02 cm−1. The following parameters were obtained for the state: D0 = 301.829 ± 0.015 cm−1, De = 333.69 ± 0.10 cm−1, Te = 8183.12 ± 0.12 cm−1.

Rates for the Electron Impact Dissociation of Molecular Hydrogen

At astrophysically relevant temperatures (below 15,000 K), electron impact dissociation of H2 occurs through the excitation of the dissociative b Σ state. We have calculated and parameterized the rates of dissociation as a function of electron temperature for the v=0-4 H2 vibrational states. The assumption that the v=0 rate approximates to the rate at local thermal equilibrium (LTE) is found to be seriously flawed. Instead, the rates are found to depend so critically on the initial vibrational level that dissociation from very high-lying vibrational levels must be included in calculations of the rate at LTE even at low temperature. An extrapolation procedure is used to approximate the rates for all of the higher vibrational levels (v=5-14), which are then used to calculate the LTE rate. The LTE rate is found to be around 2 orders of magnitude greater than the v=0 rate.

The à 2Σ+ state of Ar⋅NO studied using resonance-enhanced multiphoton and zero-kinetic-energy pulsed-field ionization spectroscopy

Resonance-enhanced multiphoton ionization (REMPI) and zero-kinetic-energy pulsed-field ionization (ZEKE-PFI) techniques have been used to study the spectroscopy of the à 2Σ+ state of Ar⋅NO. à 2Σ+–X̃ 2Π REMPI spectra of Ar⋅NO have been interpreted using two different models that have allowed assignment of the observed rovibronic transitions to be made and an estimate of the strength of the à state intermolecular potential to be determined. Simulations of the spectra have indicated that the ground vibrationless level of the à state has a linear geometry while some higher vibrational levels have a skewed T-shaped structure. The analysis has also confirmed that the à state of Ar⋅NO is very weakly bound and is non-Rydberg in character. Reported for the first time are ZEKE-PFI spectra observed via the intermediate à 2Σ+ state. No structure was detected close to the ionization threshold, although peaks observed at higher excitation energy have been assigned to transitions to high-lying vibrational levels of the Ar⋅NO+ ion. ZEKE-PFI spectra recorded via the ground vibrational level of the intermediate à state, which has a linear structure, show progressions which correlate with transitions to highly excited van der Waals stretching and bending levels; however, spectra recorded via an intermediate level with a T-shaped geometry show progressions which correlate principally with the van der Waals stretching mode. These assignments have been interpreted in terms of the large changes in intermolecular bond length and bond angle upon ionization and fully support the interpretation of the REMPI spectra. The results of the REMPI and ZEKE-PFI spectra have also been used to investigate the character of the à state and the geometry that the complex adopts in each of the vibronic levels of this state has been rationalized in terms of the possible interactions involved.