Lowest Vibrational Levels Research Articles

Near spectroscopically accurate ab initio potential energy surface for NH4(+) and variational calculations of low-lying vibrational levels.

A nine-dimensional potential energy surface (PES) for the ammonium cation has been constructed by fitting ∼30 000 AE-CCSD(T)-F12a/cc-pCVTZ-F12 points up to 32 262 cm(-1) (4.0 eV) from the minimum. The fitting using the permutation invariant polynomial-neural network method has high fidelity, with a root-mean-square error of merely 2.34 cm(-1). The low-lying vibrational energy levels of NH4(+) have been determined quantum mechanically using both Jacobi and normal coordinates, and the fundamental frequencies are in excellent agreement with available experimental data.

Lanczos wave packet propagation on coupled potential energy surfaces: the three body predissociation of rotating D3 and H3 ()

A three-dimensional wave packet method, based on Lanczos tridiagonalization of the Hamiltonian, is introduced and applied to the three-particle predissociation of rotating D3 and H3 (). The time-dependent propagation calculations on the (diabatic) ground state potential energy surfaces include the non-adiabatic transition from the excited initial state. Results for the eight lowest vibrational levels are presented as Dalitz plots and compared to momentum correlation measurements.

Configuration interaction study on electronic structures and transitional properties of excited states of GeO molecule

GeO molecule, which plays an important role in fabricating integrated optics and semiconductor components, has received much attention. However, the electronic state density of the molecule is very large, and the electric structures and transitional properties of the molecule have not been well investigated. In this work, the 18 Λ -S states correlated to the lowest dissociation limit (Ge(3Pg)+O(3Pg)) are calculated by a complete active space self-consistent field (CASSCF) method, through using the previous Hatree-Fock molecular orbitals as the starting orbitals. Furthermore, we take all configurations in the configuration interaction expansions of the CASSCF wave functions as a reference configuration, and calculate the energies of the 18Λ-S states by a high-level multireference configuration interaction method. The core-valence correlation effect of the 3d orbit of Ge atom, the scalar relativistic effect, and the Davidson correction are taken into consideration in the calculations. On the basis of the calculated potential energy curves of the bound and quasibound electronic states, the spectroscopic constants (Re, Te, ωe, ωeχe, and Be), vibrational energy levels, vibrational wave functions, and Franck-Condon factors (FCFs) are obtained by solving the radical Schrödinger equation. The computed spectroscopic constants of these electronic states are well consistent with previously available experimental results. We calculate the electric dipole moments of electronic states with different bound lengths, and analyze the influences of the variation of electron configuration on the electric dipole moment. The calculated potential energy curves indicate that the adiabatic transition energies of A1Π, 11Σ-, D1Δ, a3Π, a’3Σ+, d3Δ, and e3Σ- sates are located in a range of 26000-37000 cm-1, and the spin-orbit coupling of the states can obviously affect the corresponding vibrational wave functions. With the help of calculated spin-orbit coupling matrix elements, the perturbations of the nearby states to a3Π and A1Π are discussed in detail. Our calculation results indicate that the spin-orbit coupling between A1Π and e3Σ- states has an evident perturbation on the v’> 4 vibrational levels of A1Π, and the v’≥ 0 vibrational levels of a3Π state are perturbed by the crossing states a’3Σ+, d3Δ, e3Σ-, 11Σ-, and D1Δ. On the basis of computed transition dipole moments and FCFs of A1Π-X1Σ+ and A’1Σ+-X1Σ+ transitions, the radiative lifetimes of the six lowest vibrational levels of the two singlet excited states are computed.

UV-induced isomerization dynamics of N-methyl-2-pyridone in solution.

The photoisomerization dynamics of N-methyl-2-pyridone (NMP) dissolved in CH3CN have been interrogated by time-resolved electronic and vibrational absorption spectroscopy. Irradiation at two different wavelengths (330 or 267 nm) prepares NMP(S1) molecules with very different levels of vibrational excitation, which rapidly relax to low vibrational levels of the S1 state. Internal conversion with an associated time constant of 110(4) ps, leading to reformation of NMP(S0) molecules, is identified as the dominant (>90%) decay pathway. Much of the remaining fraction undergoes a photoinitiated rearrangement to yield two ketenes (revealed by their characteristic antisymmetric C═C═O stretching modes at 2110 and 2120 cm(-1)), which are in equilibrium. The rate of ketene formation is found to be pump-wavelength dependent, consistent with ab initio electronic structure calculations which predict a barrier on the S1 potential energy surface en route to a prefulvenic conical intersection, by which isomerization is deduced to occur. Two kinetic models-differentiated by whether product branching occurs in the S1 or S0 electronic states-are presented and used with equal success in the analysis of the experimental data, highlighting the difficulties associated with deducing unambiguous mechanistic information from kinetic data alone.

A theoretical investigation of the S2+ cation in the gas phase

The potential energy curves (PECs) of 18 lowest energy Λ-S states of the S2+ cation have been calculated using the complete active space self-consistent field method followed by the internally contracted multireference configuration interaction approach with the Davidson modification. When spin−orbit coupling is computed using the Breit−Pauli Hamiltonian with the cc-pCVTZ basis set, the 18 Λ-S states split into 56 Ω components. To improve the quality of the PECs, core−valence correlation and scalar relativistic corrections are included. All PECs are extrapolated to the complete basis set limit. Based on the PECs obtained by the icMRCI+CV+DK+Q/(CBS-56) calculations, the spectroscopic parameters of 17 Λ-S bound states and 50 Ω bound states are obtained. The transitions (including the Franck−Condon factors and radiative lifetimes) from two low-lying states to the ground state are calculated for several low vibrational levels. Analyses show that the spectroscopic parameters reported here can be expected to be reliably predicted.

Extensive spectroscopic calculations of the 21 Λ-S and 74 Ω states of the AsN molecule including the spin–orbit coupling effect

The potential energy curves (PECs) of 74 Ω states generated from the 21 Λ-S states of AsN molecule are studied for the first time for internuclear separations from 0.1 to 1.0nm. Of these 21 Λ-S states, the X1Σ+, a′3Σ+, 15Σ+, 13Δ, 13Σ−, a3Π, 15Π, 25Σ+, 35Σ+, 23Δ, 23Π, 33Π, 35Π, and A1Π states are found to be bound, and the 23Σ+, 33Σ+, 15Σ−, 15Δ, 25Δ, 25Π, and 17Σ+ states are found to be repulsive ones. The 33Π state possesses the double well. The 25Σ+, 35Σ+, 35Π, and 33Π states possess the shallow well. The a′3Σ+, 13Σ−, 23Π, 13Δ, 15Π, 25Π, 35Π, and 17Σ+ states are found to be the inverted ones with the spin–orbit coupling effect taken into account. The PECs are calculated using the CASSCF method, which is followed by the internally contracted MRCI approach with Davidson correction. Core–valence correlation and scalar relativistic corrections are included. The vibrational properties are evaluated for the 25Σ+, 35Σ+, and 35Π states and the second well of the 33Π state. The spin–orbit coupling effect is accounted for by the state interaction method with the Breit–Pauli Hamiltonian. The PECs are extrapolated to the complete basis set limit. The spectroscopic parameters are evaluated, and compared with available measurements and other theoretical results. The Franck–Condon factors and radiative lifetimes of the transitions from the a′3Σ+1, a3Π1, A1Π1, 13Δ1 and a3Π0− states to the X1Σ+0+ state are calculated for several low vibrational levels, and some necessary discussion is performed. Analyses show that the spectroscopic parameters reported in this paper can be expected to be reliably predicted ones.

Accurate spectroscopic calculations of the 12 Λ-S states and 27 Ω states of NF+ cation including the spin–orbit coupling effect

This paper studies the potential energy curves (PECs) of 27 Ω states generated from the 12 Λ-S states (X2Π, 12Σ+, 12Σ−, 22Σ−, A2Π, 12Δ, 14Σ+, 14Σ−, 24Σ−, 14Π, 24Π and 14Δ), which are attributed to the first dissociation channel of NF+ cation. Of these 12 states, only 22Σ− and 24Π are the repulsive ones, which are very different from those reported by G.-S. Kim and D. M. Hirst, Mol. Phys. 86, 1183–1193 (1995). In addition, the 12Δ and 14Σ− states are found to possess the double well. 14Σ+, 14Σ− and 14Δ are found to be the inverted states with the spin–orbit coupling effect taken into account, and 12Σ+, 12Σ−, 12Δ, 14Σ+, 24Σ− and 14Δ are found to be the weakly bound states. The PECs are calculated by the complete active space self-consistent field method, which is followed by the internally contracted multireference configuration interaction approach with Davidson correction. The convergent behaviour of the present calculations is discussed with respect to the basis set and level of theory. All the PECs are extrapolated to the complete basis set limit. Core–valence correlation and scalar relativistic corrections are included at the same time. The spin–orbit coupling effect is accounted for by the state interaction method with the Breit–Pauli Hamiltonian. The spectroscopic parameters are evaluated and compared with available measurements and other theoretical results. The effect of spin–orbit coupling on the spectroscopic parameters is discussed. The Franck–Condon factors and radiative lifetimes of the transitions from the 14Π3/2, 14Σ−3/2, 12Δ3/2 and A2Π1/2 states to the X2Π1/2 state are calculated for several low vibrational levels and some necessary discussion is done. It shows that the spectroscopic results reported in this paper can be expected to be reliably predicted ones.

Accurate calculations on the 12 electronic states and 23 Ω states of the SiBr+ cation: potential energy curves, spectroscopic parameters and spin-orbit coupling

The potential energy curves (PECs) of 23 Ω states generated from the 12 electronic states (X1 Σ +, 21 Σ +, 11 Σ −, 11 Π, 21 Π, 11 Δ, 13 Σ +, 23 Σ +, 13 Σ −, a3 Π, 23 Π and 13 Δ) are studied for the first time. All the states correlate to the first dissociation channel of the SiBr+ cation. Of these electronic states, the 23 Σ + is the repulsive one without the spin-orbit coupling, whereas it becomes the bound one with the spin-orbit coupling added. On the one hand, without the spin-orbit coupling, the 11 Π, 21 Π and 23 Π are the rather weakly bound states, and only the 11 Π state possesses the double well; on the other hand, with the spin-orbit coupling included, the a3 Π and 11 Π states possess the double well, and the 13 Σ + and 13 Σ − are the inverted states. The PECs are calculated by the CASSCF method, which is followed by the internally contracted MRCI approach with the Davidson modification. Scalar relativistic correction is calculated by the third-order Douglas-Kroll Hamiltonian approximation with a cc-pVTZ-DK basis set. Core-valence correlation correction is included with a cc-pCVTZ basis set. The spin-orbit coupling is accounted for by the state interaction method with the Breit-Pauli Hamiltonian using the all-electron aug-cc-pCVTZ basis set. All the PECs are extrapolated to the complete basis set limit. The variation with internuclear separation of the spin-orbit coupling constant is discussed in brief. The spectroscopic parameters are evaluated for the 11 bound electronic states and the 23 bound Ω states, and are compared with available measurements. Excellent agreement has been found between the present results and the experimental data. It demonstrates that the spectroscopic parameters reported here can be expected to be reliably predicted ones. The Franck-Condon factors and radiative lifetimes of the transitions from the a3 Π 0 + and a3 Π 1 states to the X1 Σ + 0+ state are calculated for several low vibrational levels, and some brief discussion has been made.

Extensive spectroscopic calculations on 12 low-lying electronic states of AlN molecule including transition properties

Using the CASSCF method followed by the internally contracted MRCI approach in combination with the correlation-consistent basis sets, the potential energy curves (PECs) are calculated for the X3Π, A3Σ-, B3Σ+, C3Π, E3Δ, a1Σ+, b1Π, c1Δ, d1Σ+, e1Π, 23Σ− and 33Σ− electronic states of AlN molecule for internuclear separations from 0.1 to 1.0 nm. All the electronic states correlate to the three dissociation channels, Al(2Pu) + N(4Su), Al(2Pu) + N(2Du) and Al(2Pu) + N(2Pu). Of these 12 electronic states, only the 23Σ− possesses the double well. The PECs determined by the internally contracted MRCI approach are corrected for size-extensivity errors by means of the Davidson correction. The convergent behavior of present calculations is observed with respect to the basis set and level of theory. The effect of core-valence correlation and scalar relativistic corrections on the spectroscopic parameters is discussed. Scalar relativistic correction calculations are performed by the third-order Douglas-Kroll Hamiltonian approximation at the level of cc-pVTZ basis set. Core-valence correlation corrections are included with a cc-pCVTZ basis set. All the PECs are extrapolated to the complete basis set limit. The spectroscopic parameters are evaluated by fitting the first ten vibrational levels when available, which are obtained by solving the ro-vibrational Schrodinger equation with the Numerov’s method. The spectroscopic parameters are compared with those reported in the literature. Excellent agreement is found between the present results and the measurements. Analyses show that the spectroscopic parameters reported in this paper can be expected to be reliably predicted ones. The Franck-Condon factors and radiative lifetimes of the transitions from the A3Σ−, B3Σ+, C3Π, a1Σ+ and b1Π electronic states to the ground state are calculated for several low vibrational levels, and some necessary discussion has been made.

Accurate calculations of spectroscopic properties for the 13 Λ–S states and the 23 Ω states of BO radical including the spin–orbit coupling effect

The spectroscopic properties of 23 Ω states generated from the 13 Λ–S states of BO radical are studied for the first time for internuclear separations from about 0.07 to 1.0nm. Of the 13 Λ–S states, each of the F2Π, 12Φ and 12Δ states is found to possess the double well. Each of the 14Π, C2Π, 12Σ− and 22Σ− states possesses one well with one barrier. The A2Π, 14Π and F2Π are the inverted states with the spin–orbit coupling effect taken into account. All the states possess the deep well except for the 12Φ. The potential energy curves (PECs) are calculated by the complete active space self-consistent field method, which is followed by the internally contracted multireference configuration interaction approach with the Davidson correction. Core–valence correlation and scalar relativistic corrections are included into the calculations. The PECs are extrapolated to the complete basis set limit. The spin–orbit coupling effect is accounted for by the state interaction approach with the Breit–Pauli Hamiltonian. The spectroscopic parameters are evaluated, and compared with the available measurements and other theoretical results. The Franck–Condon factors and radiative lifetimes of the transitions from the B2Σ+, C2Π, D2Σ+, 12Σ− and 14Π Λ–S states to the ground state are calculated for several low vibrational levels, and some necessary discussion is made. Analyses show that the spectroscopic parameters reported in this paper can be expected to be reliably predicted ones.

Rovibronic structure in slow photoelectron velocity-map imaging spectroscopy of CH2CN− and CD2CN−

We report high-resolution anion photoelectron spectra of the cryogenically cooled cyanomethide anion, CH2CN(-), and its isotopologue, CD2CN(-), using slow photoelectron velocity-map imaging (SEVI) spectroscopy. Electron affinities of 12 468(2) cm(-1) for CH2CN and 12 402(2) cm(-1) for CD2CN are obtained, demonstrating greater precision than previous experiments. New vibrational structure is resolved for both neutral species, especially activity of the ν5 hydrogen umbrella modes. The ν6 out-of-plane bending mode fundamental frequency is measured for the first time in both systems and found to be 420(10) cm(-1) for CH2CN and 389(8) cm(-1) for CD2CN. Some rotational structure is resolved, allowing for accurate extraction of vibrational frequencies. Temperature-dependent SEVI spectra show marked effects ascribed to controlled population of low-lying anion vibrational levels. We directly measure the inversion splitting between the first two vibrational levels of the anion ν5 umbrella mode in both species, finding a splitting of 130(20) cm(-1) for CH2CN(-) and 81(20) cm(-1) for CD2CN(-). Franck-Condon forbidden activity is observed and attributed to mode-specific vibrational autodetachment from the CH2CN(-) and CD2CN(-) dipole bound excited states. We also refine the binding energy of the anion dipole bound states to 39 and 42 cm(-1), respectively, for CH2CN(-) and CD2CN(-).

Radiative branching ratios for excited states of [formula omitted]YbF: Application to laser cooling

We excite YbF molecules to low-lying vibrational levels of the A2Π1/2 state, and of the nearby perturber state sometimes called [18.6]0.5. By dispersing the fluorescence, we measure branching ratios for the radiative decay to vibrational levels of the X2Σ+ state. These ratios help to determine the optimum laser cooling scheme for the molecule. Our results establish the practicality of a scheme that was previously suggested (Tarbutt et al., 2013) and show how the scheme can be modified to provide a stronger radiative cooling force.

Effects of the Chirped Pulse on Dissociation and Ionization Processes for Hydrogen Molecular Ions at Low Vibrational States

ABSTRACT The influence of a chirped laser pulse (5- fs, 800- nm) on dissociation and ionization processes for hydrogen molecular ions at low vibrational levels with different intensities has been discussed by numerically solving the one-dimensional time-dependent Schrödinger equation. By employing the “virtual detector” method, the probabilities and kinetic- energy- release spectra of dissociation and Coulomb explosion channels have been calculated. The results indicate that both the dissociation and ionization processes could be enhanced with proper chirp parameters; additionally, the dissociation process occurring at an early time in the chirped laser field is more sensitive to chirp parameters at low intensity due to the enhancement of the bond softening channel. The corresponding theoretical explanation is also provided.

Abnormal dependence of strong-field-ionization-induced nitrogen lasing on polarization ellipticity of the driving field

We experimentally investigate lasing behaviors of population-inverted N${}_{2}$ ions for the transitions between the vibrational level ($v$\ensuremath{'} = 0) of excited electronic $B$ \ensuremath{\Sigma}${}_{u}$${}^{+}$ state and the two lowest vibrational levels ($v$ = 0, 1) of the ground $X$ \ensuremath{\Sigma}${}_{g}$${}^{+}$ state in an elliptically polarized laser field. It is found that, as the polarization of the pump laser evolves from linear to circular, the lasing signal for the 0 \ensuremath{\rightarrow} 0 transition at 391 nm first increases with a maximum enhancement of \ensuremath{\sim}40% at the ellipticity of 0.3 and then decreases, whereas for the 0 \ensuremath{\rightarrow} 1 transition at 428 nm, the lasing signal decreases monotonically. This difference between the 391- and 428-nm lasing signals is ascribed to the high sensitivity of the strong-field response of the molecular ion to molecular vibrations, which indicates the possibility to control the vibrational state distribution of molecules by tuning the ellipticity of the laser pulse.

High-resolution photoassociation spectroscopy of ultracold Cs2 long-range 0−g state: The external well potential depth

High-resolution photoassociation spectroscopy is reported using a modulation spectroscopy technology in a cesium atomic magneto-optical trap. The two lowest vibrational levels have been experimentally observed which have been theoretically predicted in [Phys. Rev. A 75 052501 (2007)]. A new potential curve is obtained by using the Rydberg—Klein—Ress method with a well depth of −82.384 ± 0.026 cm−1, which is deeper than the result of previous experiment (−77.909 cm−1) and the theoretical prediction (−81.6445 cm−1).

Coherent Raman spectro-imaging with laser frequency combs

Advances in optical spectroscopy and microscopy have had a profound impact throughout the physical, chemical and biological sciences. One example is coherent Raman spectroscopy, a versatile technique interrogating vibrational transitions in molecules. It offers high spatial resolution and three-dimensional sectioning capabilities that make it a label-free tool for the non-destructive and chemically selective probing of complex systems. Indeed, single-colour Raman bands have been imaged in biological tissue at video rates by using ultra-short-pulse lasers. However, identifying multiple, and possibly unknown, molecules requires broad spectral bandwidth and high resolution. Moderate spectral spans combined with high-speed acquisition are now within reach using multichannel detection or frequency-swept laser beams. Laser frequency combs are finding increasing use for broadband molecular linear absorption spectroscopy. Here we show, by exploring their potential for nonlinear spectroscopy, that they can be harnessed for coherent anti-Stokes Raman spectroscopy and spectro-imaging. The method uses two combs and can simultaneously measure, on the microsecond timescale, all spectral elements over a wide bandwidth and with high resolution on a single photodetector. Although the overall measurement time in our proof-of-principle experiments is limited by the waiting times between successive spectral acquisitions, this limitation can be overcome with further system development. We therefore expect that our approach of using laser frequency combs will not only enable new applications for nonlinear microscopy but also benefit other nonlinear spectroscopic techniques.

Quasiclassical Trajectory Calculations of Stereodynamics and Product State Distributions in the Reaction of H with OCl

A first quasiclassical trajectory calculation for the reaction H + OCl OH + Cl, HCl + O has been carried out on the ground 11A' potential energy surface (PES) at the collision energy of 7.6 kcal/mol. The stereodynamics and product state distributions were focused on computation and analysis. It was found that, for both the OH and HCl products, the product rotational alignment and orientation were very weak. Most of the OH products are at lower vibrational levels. The HCl products dominantly populate in the ground vibrational state v'=0. Inverted rotational state distributions were found in each of the vibrational state for both the OH and HCl products. As a consequence, the title reaction takes place dominantly through an indirect mechanism involving a long-lived complex.

Resonant energy transfer between highly vibrationally excited RbH(RbD) and H2(D2)

An experimental study of vibrational relaxation and V–V and V–R energy transfer in RbH-H2 collisions and their isotopic variants has been performed. In RbH (v″=17, 18, 21)+H2, single quantum relaxation accounts for only about 30% of the total relaxation out of v″ states, and multiquantum relaxation makes significant contribution. For RbH (v″=18), Δv=2 relaxation is about twice as large as Δv=1. The significant fraction (24%) of the initial population for RbH (v″=21) prepared by overtone pumping, relaxes to much lower vibrational levels (Δv=−8). The time scales is much shorter than the known collisional lifetimes of the intervening vibrational levels and thus a sequential single-quantum relaxation mechanism can be explicitly ruled out. V–V energy transfer is suitable explanation. Energy transfer between RbD (X1Σ+v″=21–30) and D2 has been also investigated. V–R and V–V resonance behavior has been also confirmed.

Population transfer routes to the lowest vibrational level of ultracold 39K85Rb

Optimal intermediate vibrational levels for stimulated Raman transfer (SRT) through the 4 1Σ+ state of 39K85Rb to form the lowest vibrational level of the ground X 1Σ+ state from high vibrational levels of the X 1Σ+ state (formed by decay from photoassociated ultracold molecules) have been determined using a multiplicative product of a molecular beam (MB) and an ultracold molecule (UM) excitation spectrum with the appropriate frequency offset.

Vibronic origin of sulfur mass-independent isotope effect in photoexcitation of SO2and the implications to the early earth’s atmosphere

Signatures of mass-independent isotope fractionation (MIF) are found in the oxygen ((16)O,(17)O,(18)O) and sulfur ((32)S, (33)S, (34)S, (36)S) isotope systems and serve as important tracers of past and present atmospheric processes. These unique isotope signatures signify the breakdown of the traditional theory of isotope fractionation, but the physical chemistry of these isotope effects remains poorly understood. We report the production of large sulfur isotope MIF, with Δ(33)S up to 78‰ and Δ(36)S up to 110‰, from the broadband excitation of SO2 in the 250-350-nm absorption region. Acetylene is used to selectively trap the triplet-state SO2 ( (3)B1), which results from intersystem crossing from the excited singlet ( (1)A2/ (1)B1) states. The observed MIF signature differs considerably from that predicted by isotopologue-specific absorption cross-sections of SO2 and is insensitive to the wavelength region of excitation (above or below 300 nm), suggesting that the MIF originates not from the initial excitation of SO2 to the singlet states but from an isotope selective spin-orbit interaction between the singlet ( (1)A2/ (1)B1) and triplet ( (3)B1) manifolds. Calculations based on high-level potential energy surfaces of the multiple excited states show a considerable lifetime anomaly for (33)SO2 and (36)SO2 for the low vibrational levels of the (1)A2 state. These results demonstrate that the isotope selectivity of accidental near-resonance interactions between states is of critical importance in understanding the origin of MIF in photochemical systems.