OCS Molecule Research Articles

Data-Quality-Navigated Machine Learning Strategy with Chemical Intuition to Improve Generalization.

Generalizing real-world data has been one of the most difficult challenges for application of machine learning (ML) in practice. Most ML works focused on improvements in algorithms and feature representations. However, the data quality, as the foundation of ML, has been largely overlooked, also leading to the absence of data evaluation and processing methods in ML fields. Motivated by the challenge and need, we selected an important but difficult reorganization energy (RE) prediction task as a test platform, which is an important parameter for the charge mobility of organic semiconductors (OSCs), to propose a data-quality-navigated strategy with chemical intuition. We developed a data diversity evaluation based on structure characteristics of OSC molecules, a reliability evaluation method based on prediction accuracy, a data filtering method based on the uncertainty of K-fold division, and a data split technique by clustering and stratified sampling based on four molecular descriptor-associated REs. Consequently, a representative RE data set (15,989 molecules) with high reliability and diversity can be obtained. For the feature representation, a complementary strategy is proposed by considering the chemical nature of REs and the structure characteristics of OCS molecules as well as the model algorithm. In addition, an ensemble framework consisting of two deep learning models is constructed to avoid the risk of local optimization of the single model. The robustness and generalization of our model are strongly validated against different OSC-like molecules with diverse structures and a wide range of REs and real OSC molecules, greatly outperforming eight adversarial controls. Collectively, our work not only provides a quick and reliable tool to screen efficient OSCs but also offers methodological guidelines for improving the generalization of ML.

Observation of Renner-Teller and predissociation coupled vibronic intensity borrowing in dissociative electron attachment to OCS.

We use a time-of-flight-based velocity map imaging method to look into the dissociative electron attachment to a linear OCS molecule at electron beam energies ranging from 4.5 to 8.5eV. The conical time-gated wedge slice imaging method is utilized to extract fragments' slice images, kinetic energy (KE), and angular distributions, which provide a complete kinematic understanding of this experiment on the dissociative electron attachment process. We observe that the formation of S- is relatively higher than the O- product. Three distinct dissociative KE bands of S-/OCS have been observed for the 5.0 and 6.5eV resonance positions. We notice a prominent rovibrationally coupled bimodality for each KE band in the variation of the most probable KE values. When the electron energy is changed from 5.5 to 6.0eV, we observed vibronic intensity borrowing in the highest momentum band of S- via the Σ → Π symmetric dipole-forbidden transitions within the 1.5eV energy gap. Multiple peaks in the angular distributions of S- and their modeling indicate the presence of Renner-Teller vibronic splitting. Using Q-Chem's implemented complex absorbing potential-equation of motion-electron affinity coupled cluster singles and doubles aug-cc-pVDZ+4s3p level of multireference-based electronic structure theory, we confirm the presence of OCS temporary negative ion bending vibrations and Renner-Teller vibronic splittings for the Π symmetric states. Additionally, we notice the presence of a non-radiative predissociation continuum (bringing down the rotational spectrum) and speed-dependent angular anisotropy in the S- fragmentation. Our findings at the resonance of OCS at 6.5eV closely align with the prediction of vibronic intensity borrowing by Orlandi and Siebrand [J. Chem. Phys. 58, 4513 (1973)].

Excitation and ionization of OCS molecules in strong UV and NIR laser fields

Abstract Rydberg state excitation (RSE) is a highly non-linear physical phenomenon that is induced by the ionization of atoms or molecules in strong femtosecond laser fields. Here we observe that both parent and fragments (S, C, OC) of the tri-atomic molecule carbonyl sulfide (OCS) can survive strong 800 nm or 400 nm laser fields in high Rydberg states. The dependence of parent and fragment RSE yields on laser intensity and ellipticity is investigated in both laser fields, and the results are compared with those for strong-field ionization. Distinctly different tendencies for laser intensity and ellipticity are observed for fragment RSE compared with the corresponding ions. The mechanisms of RSE and strong-field ionization of OCS molecules in different laser fields are discussed based on the experimental results. Our study sheds some light on the strong-field excitation and ionization of molecules irradiated by femtosecond NIR and UV laser fields.

Rate coefficients for the rotational de-excitation of OCS by collision with He

Context. In typical molecular clouds, analyzing the physicochemical conditions with nonlocal thermodynamic equilibrium models requires knowledge of the collisional rate coefficients between the detected molecule and the most common colliders in the interstellar medium (ISM); for example H2, He, and H. The OCS molecule has been widely observed in the ISM. However, the collision data available for this species were calculated using a potential energy surface (PES) that shows differences with surfaces presented recently. Aims. The main goal of this work is to report a new set of rate coefficients for the collision of OCS with He based on a new PES computed at a high level of theory. Methods. We developed an analytical PES using a large set of ab initio energies calculated using the coupled cluster with single, double, and perturbative triple excitations (CCSD(T)) method at the completed basis set limit for the OCS+He complex. We used this surface in close-coupling calculations, and computed a new set of collisional rate coefficients for OCS and He. Results. We compare the de-excitation rate coefficients with previously available data. Furthermore, we observe a |Δj| = 1 propensity rule. Finally, we report a set of rate coefficients for the lower 39 rotational states of OCS, which is the largest set determined to date for this collision.

Circularly polarized attosecond light generation from OCS molecules irradiated by the combination of linear polarized infrared and orthogonal terahertz fields.

Researching ultrafast dynamics and creating coherent light sources will both benefit significantly from the establishment of polarization control in high-order harmonic generation (HHG). By employing the time-dependent density functional theory method, we investigate HHG of carbonyl sulfide molecules using a combination of a linear polarized infrared (IR) laser and a weaker orthogonal Terahertz (THz) field. Our findings show that by adjusting the amplitude of the THz field, the movement scale of electrons in the THz direction can be tuned, thereby one can control the harmonic intensity in the IR laser direction. This method allows for the creation of near-circularly polarized attosecond pulses. Furthermore, the ellipticity of the attosecond pulse may be changed by modifying the carrier-envelope phase of the IR laser pulse.

Strong-field ionization and AC-Stark shifted Rydberg states in OCS

We present theoretical results for intensity-dependent above-threshold ionization (ATI) spectra from oriented OCS molecules probed by intense femtosecond laser pulses with wavelengths of 800 and 400 nm. The calculations were performed using the time-dependent Schrödinger equation within the single-active-electron approximation and including multielectron polarization effects. The results capture some of the experimental findings (Yu et al 2017 J. Phys. B: At. Mol. Opt. Phys. 50 235602), in particular when considering the sensitivity of the ATI spectra on the molecular orientation. We identify characteristic features in the ATI spectra which correspond to resonant multiphoton ionization via highly-excited Rydberg states are captured by the theory.

Charge-Shifted Weak Noncovalent Interactions in the Atmospherically Important OCS Microhydrates.

Stratospheric aerosol, mainly comprising microhydrated carbonyl sulfide (OCS), is among the primary drivers of climate change. In this study, we investigate the effect of microhydration on the structure, energetics, and vibrational properties of the neutral OCS molecule using ab initio calculation, molecular electrostatic potential (MESP), topological analyses of electron density, and natural bond orbital (NBO) analyses. The complexation energy increases with the cluster size, and the first solvation shell of OCS consists of four water molecules that interact with the OCS moiety preferentially through SOCS···OW, OOCS···OW, and COCS···OW type of weak noncovalent interaction instead of the typical OOCS···H-OW and SOCS···H-OW H-bonds. These noncovalent interactions originate due to the electron shift from the water oxygen lone pair to the antibonding orbital of C═S [BD*(C═S)], sometimes via BD*(C═O), which substantially perturbs the bending mode of surrounding water molecules. The present study thus unravels the underlying relationship between the OCS atmospheric hydrolysis and the charge-shifted noncovalent interactions.

All-optical control of pendular qubit states with nonresonant two-color laser pulses

Practical methodologies for qubit controls are established by two prerequisites, i.e., preparation of a well-defined initial quantum state and coherent control of that quantum state. Here we propose a quantum control method, realized by irradiating nonresonant nanosecond two-color (ω and 2ω) laser pulses to molecules in the pendular (field-dressed) ground state. The two-color field nonadiabatically splits the initial pendular ground state |tilde{0},tilde{0}rangle to a superposition state of |tilde{0},tilde{0}rangle and |tilde{1},tilde{0}rangle , whose relative probability amplitudes can be controlled by the peak intensity of one wavelength component (ω) while the peak intensity of the other component (2ω) is fixed. The splitting of the quantum paths is evidenced by observing degrees of orientation of ground-state-selected OCS molecules by the velocity map imaging technique. This quantum control method is highly advantageous because any polar molecule can be controlled regardless of the molecular energy structures.

Stronger orientation of state-selected OCS molecules with relative-delay-adjusted nanosecond two-color laser pulses.

Using the all-optical molecular orientation technique with intense nonresonant two-color laser pulses, stronger molecular orientation |⟨cos θ2D⟩| ∼ 0.34 is achieved by employing the following two strategies: (1) carbonyl sulfide molecules lying in the lower rotational states are selected using a home-built molecular deflector and (2) the rising parts of the two wavelengths of the pump pulse are adjusted by introducing a Michelson-type delay line in the optical path. The achieved degree of molecular orientation is higher than that observed in the proof-of-principle experiment [Oda et al., Phys. Rev. Lett. 104, 213901 (2010)] by about an order of magnitude and the highest ever characterized directly by Coulomb explosion imaging with appropriate probe polarization.

Multilevel quantum interference in the formation of high-order fractional molecular alignment echoes.

We theoretically investigate the formation of the high-order fractional alignment echo in OCS molecule and systematically study the dependence of echo intensity on the intensities and time delay of the two excitation pulses. Our simulations reveal an intricate dependence of the intensity of high-order fractional alignment echo on the laser conditions. Based on the analysis with rotational density matrix, this intricate dependence is further demonstrated to arise from the interference of multiple quantum pathways that involve multilevel rotational transitions. Our result provides a comprehensive multilevel picture of the quantum dynamics of high-order fractional alignment echo in molecular ensembles, which will facilitate the development of "rotational echo spectroscopy."

Multielectron effects in strong-field ionization of the oriented OCS molecule

We present theoretical calculations of orientation-dependent total ionization yields from the highest occupied molecular orbitals of the oriented OCS molecule by solving the time-dependent Schr\"odinger equation in three dimensions. The calculations were performed within the single-active-electron approximation including multielectron polarization. The multielectron polarization term was represented by an induced dipole term which contains the polarizability of the OCS + cation parallel to the laser polarization. Upon accounting for multielectron polarization, the calculated total ionization yields and their orientation dependence are in good agreement with experimental data.

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.

Non-sequential double ionization of triatomic molecules OCS in intense laser fields

We investigated the non-sequential double ionization of the OCS molecule at both 800 nm and 1200 nm laser fields. For the double ionization with different laser wavelengths, an alternating high and low yields were observed in the yields dependence on the laser intensity. To get insight of this phenomenon, the mechanisms of the strong field double ionization were analyzed in details. An abnormal change of the mechanism was identified at 1200 nm laser fields as the laser intensity increases. With further discussions, the influence of laser wavelength on the NSDI was studied.

Theoretical investigation of potential energy surface and bound states for the N2-OCS van der Waals complex.

In this work we report an ab initio intermolecular potential energy surface and theoretically spectroscopic studies for N2-OCS complex. A four-dimensional intermolecular potential energy surface (4D PES) is constructed at the level of single and double excitation coupled-cluster method with a non-iterative perturbation treatment of triple excitations [CCSD(T)] with aug-cc-pVTZ basis set supplemented with bond functions. A global minimum corresponding to a planar and nearly T-shaped structure, which has been observed experimentally, is located at R = 3.96 Å, θ1 = 8 or 172°, θ2 = 75°, φ = 180 or 0° with a well depth of 271.078 cm-1 on the potential energy surface. The local minimum corresponding to a linear geometry is also found at R = 5.06 Å, θ1 = 2 or 178°, θ2 = 179°, φ = 0 or 180° with a well depth of 224.743 cm-1. The bound state calculations have been performed for the complex by approximating the N2 and OCS molecules as the rigid rotors. The calculated structural parameters and rotational transition frequencies are in good agreement with the experimental observed values. Based on the ab initio PES, the tunneling splitting is calculated to be 0.052 cm-1 for the ground vibrational state, which can just reproduce 64% of experimental observation (0.082 cm-1). A refined method is used to calculate the tunneling splitting, and a much better result is obtained with the value of 0.094 cm-1.

Molecules probed with a slow chirped-pulse excitation: Analytical model of the free-induction-decay signal

Most chirped-pulse experiments refer to a theoretical study from McGurk, Schmalz, and Flygare [J. Chem. Phys. 60, 4181 (1974)] which is well tailored to interpret the signals obtained with very fast chirped pulses, but is not sufficient to account for the signals in the case of slower chirped pulses used in spectroscopy to increase the signal-to-noise ratio. A theoretical study of the polarization of molecules subjected to a chirped pulse in a cell, uniform supersonic flow, or molecular beam is presented. Three degrees of approximation for the polarization are introduced and are compared with the numerical solution of the optical Bloch equations. These expressions enter the analytic expression of the free-induction-decay signal which is validated against experimental data on the rotational emission spectra of OCS molecules. A relation among the pulse duration, the line position in the chirped pulse, and the signal amplitude is proposed in the thermalized case. It assists in the optimization of the chirped-pulse parameters and in the estimation of the error associated with the line intensity.

Development of a plasma shutter applicable to 100-mJ-class, 10-ns laser pulses and the characterization of its performance.

For the purpose of preparing a sample of aligned and oriented molecules in the laser-field-free condition, we developed a plasma shutter, which enables laser pulses with 100-mJ-class, 10-ns pulse durations to be rapidly turned off within ∼150 fs. Inthis work, the residual field intensity after the rapid turn off is carefully examined by applying the shaped laser pulse to OCS molecules in the rotational ground state. Based on the comparison between the observation of alignment revivals of the OCS molecules and the results of numerical simulations, we demonstrate that the residual field intensity is actually negligible (below 0.4% of the peak intensity) and, if any, does not influence the alignment and orientation dynamics at all.

Microbial community responses determine how soil–atmosphere exchange of carbonyl sulfide, carbon monoxide, and nitric oxide responds to soil moisture

Abstract. Carbonyl sulfide (OCS) plays an important role in the global sulfur cycle and is relevant for climate change due to its role as a greenhouse gas, in aerosol formation and atmospheric chemistry. The similarities of the carbon dioxide (CO2) and OCS molecules within chemical and plant metabolic pathways have led to the use of OCS as a proxy for global gross CO2 fixation by plants (gross primary production, GPP). However, unknowns such as the OCS exchange from soils, where simultaneous OCS production (POCS) and consumption (UOCS) occur, currently limits the use of OCS as a GPP proxy. We estimated POCS and UOCS by measuring net fluxes of OCS, carbon monoxide (CO), and nitric oxide (NO) in a dynamic chamber system fumigated with air containing different mixing ratios [OCS]. Nine soils with different land use were rewetted and soil–air exchange was monitored as soils dried out to assess responses to changing moisture. A major control of OCS exchange was the total amount of available sulfur in the soil. POCS production rates were highest for soils at WFPS (water-filled pore space) >60 % and rates were negatively related to thiosulfate concentrations. These moist soils switched from a net source to a net sink activity at moderate moisture levels (WFPS 15 % to 37 %). For three soils we measured NO and CO mixing ratios at different mixing ratios of OCS and revealed that NO and potentially CO exchange rates are linked to UOCS at moderate soil moisture. High nitrate concentrations correlated with maximum OCS release rates at high soil moisture. For one of the investigated soils, the moisture and OCS mixing ratio was correlated with different microbial activity (bacterial 16S rRNA, fungal ITS RNA relative abundance) and gene transcripts of red-like cbbL and amoA.

Exit-channel recoil resonances by imaging the photodissociation of single quantum-state-selected OCS molecules

In a recent letter [Phys. Rev. Lett. 118, 253001 (2017)] we have described how studies of the recoil velocity distribution in the photodissociation of OCS in the energy interval 42 600--42 900 ${\mathrm{cm}}^{\ensuremath{-}1}$ revealed an unexpected behavior: the recoil velocity distribution of only the lowest-kinetic-energy photofragments exhibited rapid, resonantlike variations with energy and caused complete inversion of the recoil direction. Periodic orbit analysis and quantum nonadiabatic calculations unveiled the existence of a resonance state localized at large bending angles towards the exit of the dissociation channel. In this article, we present an extensive theoretical study and we show how the fingerprints of these resonances are identified by the analysis of the nonadiabatic transitions and the stereodynamics of photofragments trajectories. Additionally, the experimental study is extended to a second photolysis energy region, 43 300--43 650 ${\mathrm{cm}}^{\ensuremath{-}1}$, where a similar rapid variation of the recoil direction is detected. The energy separation between this second resonance region and the one previously reported is $\ensuremath{\sim}800\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$, which is twice the calculated period of the localized resonant state, offering a second point of convergence between the experiment and the theory.

The He2-OCS complex: Comparison between theory and experiment

OCS is an ideal probe for quantum solvation effects in cold helium clusters. He2-OCS is the “second step” in going from a single OCS molecule to a large doped superfluid helium cluster. Here assignment of the spectrum of He2-OCS is significantly extended to higher values of J, K, and vt (the low frequency torsional vibration). The observation of a new infrared band, OCS ν1 + ν3, taken together with the known ν1 band, enables assignments to be verified by comparing ground state combination differences. Relatively straightforward scaling of previously calculated theoretical energy levels gives a remarkably good fit to experiment.

Field-free molecular orientation of nonadiabatically aligned OCS

We investigate an enhancement of the orientation of OCS molecules by irradiating them with a near IR (ω) ultrashort laser pulse for alignment followed by another ultrashort laser pulse for orientation, which is synthesized by a phase-locked coherent superposition of the near IR laser pulse and its second harmonic (2ω). On the basis of the asymmetry in the ejection direction of S3+ fragment ions generated by the Coulomb explosion of multiply charged OCS, we show that the extent of the orientation of OCS is significantly enhanced when the delay between the alignment pulse and the orientation pulse is a quarter or three quarters of the rotational period. The recorded enhanced orientation was interpreted well by a numerical simulation of the temporal evolution of a rotational wave packet prepared by the alignment and orientation pulses.