Lowest Vibrational States Research Articles

Quantum state-to-state nonadiabatic dynamics of the charge transfer reaction H+ + NO(X2Π) → H + NO+(X1Σ+): Influence of ro-vibrational excitation of NO

Quantum state-to-state nonadiabatic dynamics of the charge transfer reaction H+ + NO(X2Π, vi = 1, 3, ji = 0, 1) → H + NO+(X1Σ+) has been studied based on the recently constructed diabatic potential energy matrix. It was found that the vibrational excitation of reactant NO inhibits the reactivity, while the rotational excitation of reactant NO has little effect on the reaction probability. These attributes were also observed in the semi-classical trajectory calculations employed in the adiabatic representation. Such an inhibitory effect of the vibrational excitation of reactant NO was owing to lower accessibility of the conical intersection and avoided crossing regions, which are located in the wells with respect to the Π diabat, as evidenced by the analysis of the population of the time-independent wave functions. Calculated vibrational state distributions of the product show that the decrease of the reaction mainly leads to the less formation of low vibrational states (vf < 6), and the product vibrational state distributions are more evenly populated for vi = 1 and 3, suggesting a non-statistical behavior. However, the overall shapes of the product rotational distributions remain unchanged, indicating that the redistribution of energy into the rotation of product NO is sufficient in the charge transfer process between H+ and NO. While the reaction is dominated by the forward and backward scattering in differential cross sections (DCSs), consistent with the complex-forming mechanism, a clear forward bias in the DCSs appears, indicating that the occurrence of the reaction is not sufficiently long to undergo the whole phase space of the interaction configurations.

Spectral extension of two glycolic acid conformers into the submillimeter regime

The rotational spectrum of glycolic acid has been extended to frequencies from 318 to 1000 GHz. Analysis of this spectrum builds upon previous experimental and theoretical studies performed on glycolic acid conformers. Extensive new assignments were made for the ground vibrational state of the SSC conformer of glycolic acid in addition to the two lowest vibrational states. Assignments were also expanded for the AAT conformer of glycolic acid. This work improves the precision of some rotational constants and nearly all of the centrifugal distortion constants for each conformer and vibrational state. The spectral predictions based on these refined parameters will facilitate the search for glycolic acid in the interstellar medium at frequencies covered by submillimeter observatories.

Improved quantum yield of thermally activated delayed fluorescence by nanoconfinement in organophilic octosilicate

A hybrid of a thermally activated delayed fluorescent dye (1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene, designated as 4CzIPN) and an organophilic layered silicate (dioleyldimethylammonium-octosilicate) was synthesized to achieve high photoluminescence quantum yield (0.71) of the dye, which is the critical factor in device application. Absorption, photoexcitation, and luminescence spectra suggested that the molecular conformation of 4CzIPN in the organophilic silicate enabled the utilization of the S0 → S1 transition efficiently. Furthermore, thanks to the flexible assembly of the dioleyldimethylammonium moieties, 4CzIPN was dispersed in the hybrid to suppress concentration quenching. Emission spectra and photoluminescence lifetimes in ambient and N2 atmosphere revealed that the photoluminescence quantum yield increased by the utilization of transition to a lower vibrational state and protection of a triplet state of 4CzIPN from oxygen in air in the organophilic silicate.

Photodissociation study of CO2 on the formation of state-correlated CO(X1Σ+, v) with O(3P2) photoproducts in the low energy band centered at 148 nm.

The spin-forbidden O(3P2) + CO(X1Σ+, v) channel formed from the photodissociation of CO2 in the low energy band centered at 148nm is investigated by using the time-sliced velocity-mapped ion imaging technique. The vibrational-resolved images of the O(3P2) photoproducts measured in the photolysis wavelength range of 144.62-150.45nm are analyzed to give the total kinetic energy releases (TKER) spectra, CO(X1Σ+) vibrational state distributions, and anisotropy parameters (β). The TKER spectra reveal the formation of correlated CO(X1Σ+) with well resolved v = 0-10 (or 11) vibrational bands. Several high vibrational bands that were observed in the low TKER region for each studied photolysis wavelength exhibit a bimodal structure. The CO(X1Σ+, v) vibrational distributions all present inverted characteristics, and the most populated vibrational state changes from a low vibrational state to a relatively higher vibrational state with a change in the photolysis wavelength from 150.45 to 144.62nm. However, the vibrational-state specific β-values for different photolysis wavelengths present a similar variation trend. The measured β-values show a significant bulge at the higher vibrational levels, in addition to the overall slow decreasing trend. The observed bimodal structures with mutational β-values for the high vibrational excited state CO(1Σ+) photoproducts suggest the existence of more than one nonadiabatic pathway with different anisotropies in the formation of O(3P2) + CO(X1Σ+, v) photoproducts across the low energy band.

Enhancing Strong-Field Dissociation of H2+ in Helium Nanodroplets

We investigate the above-threshold multiphoton ionization of H_{2} embedded in superfluid He nanodroplets driven by ultraviolet femtosecond laser pulses. We find that the surrounding He atoms enhance the dissociation of in-droplet H_{2}^{+} from lower vibrational states as compared to that of isolated gas-phase molecules. As a result, the discrete peaks in the photoelectron energy spectrum correlated with the HHe^{+} from the dissociative in-droplet molecule shift to higher energies. Based on the electron-nuclear correlation, the photoelectrons with higher energies are correlated to the nuclei of the low-vibrationally excited molecular ion as the nuclei share less photon energy. Our time-dependent nuclear wave packet quantum simulation using a simplified He-H_{2}^{+} system confirms the joint contribution of the driving laser field and the neighboring He atoms to the dissociation dynamics of the solute molecular ion. The results strengthen our understanding of the role of the environment on light-induced ultrafast dynamics of molecules.

Excitation wavelength dependent S1-state decay dynamics of 2-aminopyridine and 3-aminopyridine.

The decay dynamics of 2-aminopyridine and 3-aminopyridine excited to the S1 state is investigated using femtosecond time-resolved photoelectron imaging. The lifetime of the S1 state for both molecules shows a rapid decrease with the increase of the vibrational energy. It is shown that, besides intersystem crossing to the lower-lying triplet state of T1, the decay to the ground state (S0) via internal conversion through a conical intersection plays an increasingly important role and becomes dominant for vibrational states well above the S1 state origin. The comparison between 2-aminopyridine and 3-aminopyridine suggests that the intramolecular hydrogen bonding between a hydrogen atom of the NH2 group and the heterocyclic nitrogen atom in 2-aminopyridine effectively hinders the ring deformation at lower vibrational states which is required for the wavepacket to reach the S1/S0 conical intersection, and therefore slows down the S1 to S0 internal conversion.

Nonadiabatic quantum dynamics of the charge transfer reaction H+ + NO(X2Π) → H + NO+(X1Σ+).

Nonadiabatic quantum dynamics of the charge transfer (CT) reaction H+ + NO(X2Π) → H + NO+(X1Σ+) is investigated on a new diabatic potential energy matrix (PEM) including the 12A' and 22A' states of HNO+/HON+ at the multireference configuration interaction level with Davidson correction using a large basis set. The diabatization of the two coupled states was achieved by the adiabatic-to-diabatic transformation with a mixing angle and the final diabatic PEM was obtained by fitting each matrix element separately using a three-dimensional cubic spline interpolation including more than 22 000 ab initio points. The reaction was found to be dominated by the resonances supported by the double well associated with HNO+ and HON+ species, manifested by the oscillatory structures in the reaction probabilities and product rotational distributions. The product vibrational states were highly excited due to the large exothermicity of the reaction. Consistent with the complex-forming mechanism, the differential cross sections (DCSs) were found to be dominated by the forward and backward scatterings. A clear forward bias in the vibrational state resolved DCSs suggests that the non-statistical behavior of the reaction mainly comes from the low vibrational states of the product. In addition, the rate constants of the reaction in the temperature range from 50 to 500 K were computed for the first time and found to be in fairly good agreement with the available experimental results at 300 K. In particular, compared to other reactions involving neutral species in this system including N, O, and H atoms, such a CT reaction was found to be much more reactive, which has rate constants more than thirty times larger.

Photodissociation dynamics of CO2 + hv → CO(X1Σ+) + O(1D2) via the 3P1Πu state.

The vacuum ultraviolet (VUV) photodissociation of CO2 is important to understand the primary photochemical processes of CO2 induced by solar VUV excitation in the Earth's atmosphere. Here, we report a detailed study of vibrational-state-specific photodissociation dynamics of the CO(X1Σ+) + O(1D2) channel via the 3P1Πu state by using the time-sliced velocity-mapped ion imaging apparatus combined with the single VUV photoionization detection scheme. By recording the sliced images of the O(1D2) photoproducts formed by VUV photoexcitation of CO2 to the individual vibrational structure of the 3P1Πu state, both the vibrational state distributions of the counterpart CO(X1Σ+) photoproducts and the vibrational-state-specific product anisotropy parameters (β) are determined. The experimental results show that photodissociation of CO2 at 108.22, 107.50, 106.10, and 104.76nm yields less anisotropic (β > 0) and inverted distributed CO(X1Σ+, v) photoproducts. The possible dissociation mechanism for the CO(X1Σ+) + O(1D2) channel may involve the non-adiabatic transition of excited CO2* from the initially prepared state to the 31A' state with potential energy barriers. While at 108.82 and 107.35nm, the vibrational distributions are found to have the population peaked at a low vibrational state, and the anisotropy parameters turn out to be negative. Such variation indicates the possibility of another non-adiabatic dissociation pathway that may involve Coriolis-type coupling to the low-lying dissociative state. These observations show sclear evidence of the influence of the initially vibrational excitations on the photodissociation dynamics of CO2 via the 3P1Πu state.

Computational study on the reaction collisions for the state-to-state process of N(4 S)+NO(2Π)→O(3 P)+N2(X 1Σ+ g)

Quasi-classical trajectory method has been employed in the theoretical calculations for the state-to-state processes of the reaction N(4 S)+NO(2Π)→O(3 P)+N2(X 1Σ+ g) over a temperature range of 300 K ≤ T ≤ 10,000 K on Global triplet potential energy surface (PES) for N2O system. The thermal rates calculated for the N + NO→O + N2 reaction show a great agreement with the previous theoretical and experimental results. The results obtained herein fill the gaps in the existing data for the state-to-state processes in the N2O system and could be applied to large temperature ranges relevant to the model of hypersonic gas flows. In addition, the vibrational relaxation rate coefficients of the non-reactive collision between N atom and NO molecule in the low vibrational excited state were calculated and reported.

Understanding the Large Kinetic Isotope Effect of Hydrogen Tunneling in Condensed Phases by Using Double-Well Model Systems.

In recent years, many experiments have shown large kinetic isotope effects (KIEs) for hydrogen transfer reactions in condensed phases as evidence of strong quantum tunneling effects. Since accurate calculation of the tunneling dynamics in such systems still present significant challenges, previous studies have employed different types of approximations to estimate the tunneling effects and KIEs. In this work, by employing model systems consisting of a double-well coupled to a harmonic bath, we calculate the tunneling effects and KIEs using the numerically exact hierarchical equations of motion (HEOM) method. It is found that hydrogen and deuterium transfer reactions in the same system may show rather different behaviors, where hydrogen transfer is dominated by tunneling between the two lowest vibrational states and deuterium transfer is controlled by excited vibrational states close to the barrier top. The simulation results are also used to test the validity of various approximate methods. It is shown that the Wolynes theory of dissipative tunneling gives a good estimation of rate constants in the over-the-barrier regime, while the nonadiabatic reaction rate theory based on the Landau-Zener formula is more suitable for deep tunneling reactions.

The Synchrotron-based Far-infrared Spectrum of Glycolaldehyde

Abstract Glycolaldehyde (GA) has been observed toward several different sources, with a broad range of rotational temperatures (8–300 K). At the high end, the temperature is comparable to the energy of the lowest vibrational states of GA, making the vibrational contribution to the partition function significant. Here, we report an analysis of the high-resolution far-infrared spectrum of GA, which features a plethora of well-resolved lines from 170–430 cm−1 (13–5 THz). We focus on the three fundamental vibrational bands in this range, i.e., the symmetric ν 12 bend at 282 cm−1, and the asymmetric ν 17 and ν 18 torsions at 360 and 208 cm−1, respectively. We assigned 23,266 transitions to 13,999 lines within these bands, which, when combined with the previously reported microwave and millimeter-wave spectra, allowed for refinement of the vibrationally excited rotational constants, and accurate determination of their band origins. Additionally, the assignment of a number of lines in several hot bands that are significantly populated at 300 K allowed for determination of their band origins. The rotational constants reported here should be useful in searches of vibrationally excited GA toward warm sources, and the accurately determined band origins allow for refinement of the vibrational partition function, and therefore column density, for a given excitation temperature.

Rovibrationally state-specific collision model for the O2(Σg-3) + O(P3) system in DSMC.

A rovibrationally state-specific collision model for the O2(Σg-3)+O(P3) system is presented for direct simulation Monte Carlo, including rotation-vibration-translation energy transfer, exchange, dissociation, and recombination processes. The two-step binary collision approach is employed to model recombination reactions. Two available cross section databases by Andrienko/Boyd and Esposito/Capitelli are employed for the rovibrationally resolved model (rv-STS) and vibrationally resolved model (v-STS), respectively. The difference between rv-STS and v-STS comes from two contributions: the multisurface factor of dissociation (fMS) and the rotational averaging process. The dissociation cross section with the constant fMS is typically larger than with the variable fMS, especially for the low vibrational energy states. On the other hand, the cross sections resulting from the rotationally averaged database are found to underpredict the dissociation rate coefficient at low temperatures. In the rovibrational heating case, the rv-STS predicts faster relaxation than the v-STS, which also shows a lower quasi-steady-state temperature than v-STS. In the rovibrational cooling case, the rv-STS shows a faster relaxation than v-STS, which also presents a thermal non-equilibrium between rovibrational and translational mode during the cooling process.

Theoretical study on the electronic structure of NaS including spin-orbit coupling

The 19 Λ-S states and the low-lying Ω states of NaS molecule are computed by using the multireference configuration method (MRCI) including spin-orbit coupling (SOC), core-valence correlation (CV), scalar relativistic effects and Davidson (+Q) correction. The potential energy curves (PECs), spectroscopic constants and dipole moments are obtained. The predissociation mechanism of A2Σ+ is investigated in detail with aid of the SOC matrix elements. Finally, the transition properties of the NaS molecule including the Franck-Condon Factors (FCFs), transition dipole moments (TDMs), and the spontaneous radiative lifetimes of lower vibrational states are investigated. Our computational results will help to understand the spectroscopic and properties for further experimental studies of NaS.

The low energy phonon modes of the hydrogenated and deuterated π-conjugated system 7,7,8,8-tetracyanoquinodimethane: an inelastic neutron scattering study.

The organic acceptor, 7,7,8,8-tetracyanoquinodimethane (TCNQ), has been the subject of much research over the past few decades. Due to the π-conjugation of the quinodal structure, TCNQ as well as TCNQ based charge transfer compounds, exhibit some remarkable conducting properties. We present a study of the neutral TCNQ using inelastic neutron spectroscopy (INS) and show the first temperature dependent INS data collected on TCNQ allowing us to probe the temperature dependence of the low energy vibrational states, which have been shown to have an effect on charge delocalisation. Computational calculations have been used to help understand the data and the combination with the INS allows us to understand the phonon states. A complimentary experiment on deuterated TCNQ was also performed that allows a brief comparison of the isotopic substitution. This work utilises novel techniques to aid the understanding of the bulk properties of TCNQ in its neutral state that can be fed into work on other TCNQ based materials, including the exploration of deuteration as a technique to tune the properties of the parent compound.

Quantum Dynamics Studies of the Significant Intramolecular Isotope Effects on the Nonadiabatic Be+(2P) + HD → BeH+/BeD+ + D/H Reaction.

Quantum time-dependent wave packet dynamics studies on the nonadiabatic Be+(2P) + HD → BeH+/BeD+ + D/H reaction are performed for the first time employing recently constructed diabatic potential energy surfaces. Strong intramolecular isotope effects and unusual results are presented, which are attributed to the dynamic effects of shallow wells induced by avoided crossing on the diagonal V22d surface. The BeH+ + D and BeD+ + H channels are dominated by high-J and low-J partial waves, respectively. The BeD+/BeH+ branching ratio is larger than 10 at low energy and gradually decreases with increasing collision energy. The BeH+ product is primarily distributed at low vibrational states, whereas there exists an obvious population inversion of vibrational states on the BeD+ product. The results of differential cross sections suggest that the formation of the BeH+ + D channel favors a direct reaction process, while the BeD+ + H channel is mainly generated by the complex-forming mechanism.

Relativistic treatment of alkaline earth dimers in the presence of non-central molecular potential in N-dimensions

Abstract Within the framework of relativistic theory, N-dimensional non-central Morse potential as anharmonic model is considered thoroughly to describe the internuclear motion of alkaline earth dimers in the different electronic states. We illustrate the surface plots of alkaline earth dimers to examine the effect of angular potential, due to existence of molecular systems in which spherical symmetry disappears. Also, the contribution of angle dependent interaction to the relativistic energy spectra has been investigated in N-dimensions. We determine the relativistic vibrational transition frequencies in the lower vibrational states for the X 1 Σ g + ground state of 24 Mg 2 , 40 Ca 2 , 24 Mg 40 Ca and A 1 Σ u + excited state of 88 Sr 2 alkaline earth diatomic molecules. The theoretical results have been compared with Rydberg-Klein-Rees (RKR) and the inverted perturbation approach (IPA) experimental data. We also discussed the validity of Pekeris approximation around the equilibrium distance as well as the repulsive and attractive regions for alkaline earth dimers.

A quantum mechanical study of the astrophysically important reaction Li + HD+ (v = 0,1, j = 0): the effect of reagent vibrational and translational excitation on the angular distributions of LiH and LiD

Accurate quantum reactive calculations for the reaction Li + HD (, ) have been performed on the potential energy surface of Martinazzo et al. [J. Chem. Phys. 119 (21), 11241 (2003)] with the time-dependent wave packet coupled-channel approach. The reaction probabilities reveal that the Coriolis coupling effect is significant to the title reaction particularly for the larger mass product LiD. The total differential cross-sections for LiH and LiD indicate that vibrational and translational excitation of HD stimulate products scatter in the forward regions. For the reaction, the products LiH and LiD in low vibrational states show pronounced sideways scattering, while products in higher vibrational states scatter preferentially towards forward/backward regions. For the reaction, the scattering in the forward regions is more intense than in the backward regions for both products in each vibrational state. An analysis of the total and state-resolved opacity functions reveal that the reactivity of the title reaction is promoted by high collisions, and that the angular distributions of the products correlate strongly with low and high J values.

Wavelength dependent photodissociation of OCS via F 31Π Rydberg state: CO(X1Σ+)+S(1D2) product channel

The vacuum ultraviolet photodissociation of OCS via the F 31Π Rydberg states was investigated in the range of 134–140 nm by means of the time-sliced velocity map ion imaging technique. The images of S(1D2) products from the CO(X1Σ+)+S(1D2) dissociation channel were acquired at five photolysis wavelengths, corresponding to a series of symmetric stretching vibrational excitations in OCS(F 31Π, υ1=0–4). The total translational energy distributions, vibrational populations and angular distributions of CO(X1Σ+, υ) coproducts were derived. The analysis of experimental results suggests that the excited OCS molecules dissociate to CO(X1Σ+) and S(1D2) products via non-adiabatic couplings between the upper F 31Π states and the lower-lying states both in the C∞υ and Cs symmetry. Furthermore, strong wavelength dependent behavior has been observed: the greatly distinct vibrational populations and angular distributions of CO(X1Σ+, υ) products from the lower (υ1=0–2) and higher (υ1=3, 4) vibrational states of the excited OCS(F 31Π, υ1) demonstrate that very different mechanisms are involved in the dissociation processes. This study provides evidence for the possible contribution of vibronic coupling and the crucial role of vibronic coupling on the vacuum ultraviolet photodissociation dynamics.

Fundamental Analysis of Singular and Resonance Phenomena in Vibrational Polyads of the Difluorosilylene Molecule

The singular structure of lower vibrational states of the difluorosilylene molecule (up to four total excitation quanta) is studied by expansion of energies of each state into series of the high-order Rayleigh–Schrodinger perturbation theory and analysis of their implicit properties of multiple-valuedness using Pade–Hermite fourth-order approximants. The quartic surface of potential energy in dimensionless normal coordinates is calculated quantum-mechanically at the MP2/cc-pVTZ level. It is shown that one of values of multiple-valued approximants reproduces the variational solution with a high accuracy, while other values (beginning with the fourth polyad) in many cases coincide with energies of other states of the same polyad. The Fermi and Darling–Dennison resonances are analyzed based on facts of coincidence of singular complex branch points of the approximants for mutually interacting states inside a unit circle or near it on the complex plane. It is found that a pair of states can have several coinciding branch points of the solutions (in particular, inside the unit circle). A conclusion is made that this approach is an effective method for the determination of the polyad structure of vibrational states. Calculation parameters necessary for the reproducibility of key results are selected. The calculations are carried out by means of a Fortran-based software package using an arithmetic calculation package with a long mantissa of real numbers (200 digits).

Exploring the excited states of the GeH+ radical cation including spin-orbit interaction: A revisited study

In this paper, we have carried out high-level ab initio calculations on the electronic states of GeH+ with the configuration interaction method. The spin-orbit coupling (SOC), core-valence correlation (CV), scalar relativistic effects and Davidson correction (+Q) are included. The potential energy curves (PECs) of 13 Λ-S correlated with the four lowest dissociation limits and 32 Ω electronic states generated from those Λ-S states are obtained. Our results indicate that the first 3Σ− and second 3Π states are adiabatically correlated with the dissociation limit Ge(3Pg) + H+(1S), which is different from the previously reported Ge+(4Pg) + H(2Sg). From the computed PECs, the spectroscopic constants of the Λ-S and Ω states are determined, which are in good agreement with previous experiments. The dipole moments (DMs) for Λ-S electronic states are also investigated. With the help of spin-orbit coupling matrix involving the 13Σ− and 23Π states, the intricate couplings related with the crossing states are revealed, and the weak predissociation for ν' ≥0 vibrational levels of 13Σ− and the perturbations for vibrational levels of 21Σ+ (ν' ≥1) and 11Δ (ν' ≥0) states are analyzed. Finally, the transition properties of five transitions are predicted, including the Franck-Condon Factors (FCFs), transition dipole moments (TDMs), and the spontaneous radiative lifetimes of lower vibrational states. This study will improve our comprehension on the detailed electronic structure and spectroscopy of GeH+ radical cation.