GPR177 promotes gastric cancer proliferation by suppressing endoplasmic reticulum stress-induced cell death.

Gastric cancer is the fourth most common cancer worldwide. Despite the high incidence of gastric cancer, efficient chemotherapy treatments still need to be developed. In this study, we examined the anticancer effects of endoplasmic reticulum (ER) stress inducer tunicamycin in gastric cancer. Previously, we found that overexpression of WLS1/GPR177 correlated with poor prognosis in patients with gastric cancer. Furthermore, tunicamycin treatment downregulated GPR177 expression in a dose-dependent manner. GPR177 transports WNT ligand from ER to the plasma membrane, mediating its secretion to the extracellular matrix. In gastric cancer cells, GPR177 preferentially localizes to the ER. Small interfering RNA-mediated knockdown of GPR177 leads to sensitization to ER stress and induces apoptosis of cancer cells along with tunicamycin treatment. GPR177 suppression promoted the ER stress-mediated proapoptotic pathway, such as PERK-CHOP cascade. Furthermore, fluorouracil treatment combined with tunicamycin dramatically reduced cancer cell proliferation. Efficacy of tunicamycin chemotherapy treatments depended on GPR177 expression in gastric cancer cell lines. Together, our results indicate that ER stress can potentiate anticancer effects and suggest GPR177 as a potential gastric cancer therapeutic target.

Gender differences among medical students, house staff, and faculty physicians at high risk for suicide: A HEAR report.

BACKGROUND: In comparison with the general population, physicians, and physicians-in-training are at greater risk for suicide. Although key gender differences in suicide risk factors and behaviors have been identified in the general population, the extent to which these differences apply to physicians and physicians-in-training is unclear. Here, we aimed to identify gender differences in risk factors, clinical presentation, and help-seeking behaviors of medical students, house staff, and physician faculty at high risk for suicide. METHODS: We explored gender differences among 450 physicians and trainees meeting criteria for high suicide risk on anonymous online questionnaires completed between 2009 and 2017. RESULTS: High-risk female trainees and physicians had higher mean Patient Health Questionnaire-9 (PHQ-9) scores compared with the males (11.1, standard deviation [SD] 5.1 vs. 9.8, SD 4.7) and were more likely to endorse feeling worried (73.8% vs. 61.2%), irritable (60.4% vs. 49.4%), and stressed (79.6% vs. 70%). High-risk male trainees and physicians were more likely than females to endorse suicidal thoughts (31.2% vs. 22.1%), intense anger (24.3% vs. 16.1%), drinking too much (31.2% vs. 22.3%), and recreational drug or prescription medication use without clinically appropriate follow-up (9.4% vs. 4.3%). There were no gender differences in help-seeking behaviors. CONCLUSIONS: This is the first study to report gender differences among risk factors, presentation, and help-seeking behaviors of physicians, and trainees at high risk for suicide. Our findings are mostly consistent with those of the general population and show that only a minority of at-risk men and women in healthcare sought treatment, highlighting the importance of intervention and suicide prevention in this population.

A functional magnetic resonance imaging investigation of visual hallucinations in the human striate cortex.

PURPOSE: Human beings frequently experience fear, phobia, migraine and hallucinations, however, the cerebral mechanisms underpinning these conditions remain poorly understood. Towards this goal, in this work, we aim to correlate the human ocular perceptions with visual hallucinations, and map them to their cerebral origins. METHODS: An fMRI study was performed to examine the visual cortical areas including the striate, parastriate and peristriate cortex in the occipital lobe of the human brain. 24 healthy subjects were enrolled and four visual patterns including hallucination circle (HCC), hallucination fan (HCF), retinotopy circle (RTC) and retinotopy cross (RTX) were used towards registering their impact in the aforementioned visual related areas. One-way analysis of variance was used to evaluate the significance of difference between induced activations. Multinomial regression and and K-means were used to cluster activation patterns in visual areas of the brain. RESULTS: Significant activations were observed in the visual cortex as a result of stimulus presentation. The responses induced by visual stimuli were resolved to Brodmann areas 17, 18 and 19. Activation data clustered into independent and mutually exclusive clusters with HCC registering higher activations as compared to HCF, RTC and RTX. CONCLUSIONS: We conclude that small circular objects, in rotation, tend to leave greater hallucinating impressions in the visual region. The similarity between observed activation patterns and those reported in conditions such as epilepsy and visual hallucinations can help elucidate the cortical mechanisms underlying these conditions. Trial Registration 1121_GWJUNG.

Time-dependent wave packet averaged vibrational frequencies from femtosecond stimulated Raman spectra.

Femtosecond stimulated Raman spectroscopy (FSRS) on the Stokes side arises from a third order polarization, P(3)(t), which is given by an overlap of a first order wave packet, |Ψ2(1)(pu,t)>, prepared by a narrow band (ps) Raman pump pulse, Epu(t), on the upper electronic e2 potential energy surface (PES), with a second order wave packet, <Ψ1(2)(pr(∗),pu,t)|, that is prepared on the lower electronic e1 PES by a broadband (fs) probe pulse, Epr(t), acting on the first-order wave packet. In off-resonant |FSRS, Ψ2(1)(pu,t)> resembles the zeroth order wave packet |Ψ1(0)(t)> on the lower PES spatially, but with a force on |Ψ2(1)(pu,t)> along the coordinates of the reporter modes due to displacements in the equilibrium position, so that <Ψ1(2)(pr(∗),pu,t)| will oscillate along those coordinates thus giving rise to similar oscillations in P(3)(t) with the frequencies of the reporter modes. So, by recovering P(3)(t) from the FSRS spectrum, we are able to deduce information on the time-dependent quantum-mechanical wave packet averaged frequencies, ω̄j(t), of the reporter modes j along the trajectory of |Ψ1 (0)(t)>. The observable FSRS Raman gain is related to the imaginary part of P(3)(ω). The imaginary and real parts of P(3)(ω) are related by the Kramers-Kronig relation. Hence, from the FSRS Raman gain, we can obtain the complex P(3)(ω), whose Fourier transform then gives us the complex P(3)(t) to analyze for ω̄j(t). We apply the theory, first, to a two-dimensional model system with one conformational mode of low frequency and one reporter vibrational mode of higher frequency with good results, and then we apply it to the time-resolved FSRS spectra of the cis-trans isomerization of retinal in rhodopsin [P. Kukura et al., Science 310, 1006 (2005)]. We obtain the vibrational frequency up-shift time constants for the C12-H wagging mode at 216 fs and for the C10-H wagging mode at 161 fs which are larger than for the C11-H wagging mode at 127 fs, i.e., the C11-H wagging mode arrives at its final frequency while the C12-H and C10-H wagging modes are still up-shifting to their final values, agreeing with the findings of Yan et al. [Biochemistry 43, 10867 (2004)].

Characterization of swiftlet edible bird nest, a mucin glycoprotein, and its adulterants by Raman microspectroscopy.

Edible bird's nest (EBN) is made from the glutinous salivary secretion of highly concentrated mucin glycoprotein by swiftlets (genus Aerodramus or Collocalia) native to the Indo-Pacific region. The unique Raman spectrum of EBN has vibrational lines that can be assigned to peptides and saccharides in the glycoprotein, and it can be used to screen for adulteration. The common edible adulterants classified into two types. Type I adulterants, such as fish bladder, pork skin, karaya gum, coralline seaweed, agar strips, and tremella fungus, were solids which adhered externally on the surface of the EBN cement. They can usually be detected with a microscope based on differences in the surface structure. Type II adulterants were water soluble substances such as saccharides (e.g., glucose, sucrose), polypeptides (e.g., hydrolyzed collagen) and salts (e.g. monosodium glutamate) which can be readily soaked up by the EBN hydrogel when moist and adsorbed internally in the EBN cement matrix forming a composite upon drying, making them difficult to detect visually. The present study showed that Raman microspectroscopy offers a rapid, non-invasive, and label free technique to detect both Type I and II adulterants in EBN.

Outcomes 5 years after response to rituximab therapy in children and adults with immune thrombocytopenia.

Treatments for immune thrombocytopenic purpura (ITP) providing durable platelet responses without continued dosing are limited. Whereas complete responses (CRs) to B-cell depletion in ITP usually last for 1 year in adults, partial responses (PRs) are less durable. Comparable data do not exist for children and 5-year outcomes are unavailable. Patients with ITP treated with rituximab who achieved CRs and PRs (platelets > 150 × 10(9)/L or 50-150 × 10(9)/L, respectively) were selected to be assessed for duration of their response; 72 adults whose response lasted at least 1 year and 66 children with response of any duration were included. Patients had baseline platelet counts < 30 × 10(9)/L; 95% had ITP of > 6 months in duration. Adults and children each had initial overall response rates of 57% and similar 5-year estimates of persisting response (21% and 26%, respectively). Children did not relapse after 2 years from initial treatment whereas adults did. Initial CR and prolonged B-cell depletion predicted sustained responses whereas prior splenectomy, age, sex, and duration of ITP did not. No novel or substantial long-term clinical toxicity was observed. In summary, 21% to 26% of adults and children with chronic ITP treated with standard-dose rituximab maintained a treatment-free response for at least 5 years without major toxicity. These results can inform clinical decision-making.

Calculation of state-to-state cross sections for triatomic reaction by the multi-configuration time-dependent Hartree method.

A framework for quantum state-to-state integral and differential cross sections of triatomic reactive scattering using the Multi-Configuration Time-Dependent Hartree (MCTDH) method is introduced, where a modified version of the Heidelberg MCTDH package is applied. Parity of the system is adopted using only non-negative helicity quantum numbers, which reduces the basis set size of the single particle functions in angular degree of freedom almost by half. The initial wave packet is constructed in the space-fixed frame, which can accurately account for the centrifugal potential. By using the reactant-coordinate-based method, the product state-resolved information can be accurately extracted. Test calculations are presented for the H + H2 reactive scattering. This work demonstrates the capability of the MCTDH method for extracting accurate state-to-state integral and differential cross sections. As an efficient scheme for high-dimensional problems, the MCTDH method may be promising for the study of product state-resolved cross sections for polyatomic reactive systems.

X-ray strain tensor imaging: FEM simulation and experiments with a micro-CT.

In tissue elasticity imaging, measuring the strain tensor components is necessary to solve the inverse problem. However, it is impractical to measure all the tensor components in ultrasound or MRI elastography because of their anisotropic spatial resolution. The objective of this study is to compute 3D strain tensor maps from the 3D CT images of a tissue-mimicking phantom. We took 3D micro-CT images of the phantom twice with applying two different mechanical compressions to it. Applying the 3D image correlation technique to the CT images under different compression, we computed 3D displacement vectors and strain tensors at every pixel. To evaluate the accuracy of the strain tensor maps, we made a 3D FEM model of the phantom, and we computed strain tensor maps through FEM simulation. Experimentally obtained strain tensor maps showed similar patterns to the FEM-simulated ones in visual inspection. The correlation between the strain tensor maps obtained from the experiment and the FEM simulation ranges from 0.03 to 0.93. Even though the strain tensor maps suffer from high level noise, we expect the x-ray strain tensor imaging may find some biomedical applications such as malignant tissue characterization and stress analysis inside the tissues.

Probing non-adiabatic conical intersections using absorption, spontaneous Raman, and femtosecond stimulated Raman spectroscopy.

We present the time-frame calculated photoabsorption spectrum (ABS), spontaneous Raman excitation profile (REP), femtosecond stimulated Raman spectroscopy (FSRS) spectrum, and femtosecond stimulated Raman excitation profile (FSREP) results of a two-mode and three-mode, three-electronic-states model Hamiltonians containing conical intersections (CIs) along its two upper diabatic electronic states, e1 (dark) and e2 (bright), with and without coupling (nonadiabatic dynamics) along an asymmetric mode. For every electronic state in each model, there is one coupling mode and the rest of the modes are symmetric tuning modes. The CI appears in the Hamiltonian as off-diagonal entries to the potential term that couple the two upper states, in the form of a linear function of the coupling mode. We show that: (a) the ABS, REP, and FSREP for Stokes and anti-Stokes lines contain similar information about the e1 and e2 vibrational bands, (b) the FSRS spectra feature narrow stationary peaks and broader moving peaks contributed by the different resonant components of the third-order polarization terms from perturbation theory, and (c) a relatively strong and narrow stationary band of the allowed first overtone of the asymmetric coupling mode is observed in the Stokes FSREP in the e1 energy region with coupling to e2.

Time-dependent wave packet state-to-state dynamics of H/D + HCl/DCl reactions.

The H/D + HCl/DCl (v(0) = 0, j(0) = 0) reactions were investigated in the gas phase using the reactant coordinate based time-dependent wave packet method on the BW2 PES [W. Bian and H.-J. Werner, J. Chem. Phys. 112, 220 (2000)]. The total and state-to-state integral and differential cross sections of both the abstraction and the exchange channels were reported over the energy range from threshold to 2.0 eV. The theoretical total exchange integral cross sections agree well with Volpp's experimental measurements but differ from Polanyi's experimental results for H + DCl reaction. The theoretical total abstraction integral cross sections are more than twice as large as the experimental results from the two groups for the H + HCl/DCl reactions. For the four isotope combinations, the total exchange integral cross sections increase monotonically with collisional energy while the abstraction integral cross sections start to decrease at relatively high collision energies. And the abstraction products are predominantly backward and sideways scattered while the exchange products are almost backward scattered. For the two channels, the D + HCl reaction presents the highest reactivity, the H + DCl reaction presents the lowest reactivity, and the H + HCl and D + DCl reactions are in between with the H + HCl reaction having a slightly larger reactivity.

Calculation of strain images of a breast-mimicking phantom from 3D CT image data.

PURPOSE: Elastography is a medical imaging modality to visualize the elasticity of soft tissues. Ultrasound and MRI have been exclusively used for elastography of soft tissues since they can sensitize the tissues' minute displacements of an order of µm. It is known that ultrasound and MRI elastography show cancerous tissues with much higher contrast than conventional ultrasound and MRI. To evaluate possibility of combining elastography with x-ray imaging, we have calculated strain images of a breast-mimicking phantom from its 3D CT image data. METHODS: We first simulated the x-ray elastography using a FEM model which incorporated both the elasticity and x-ray attenuation behaviors of breast tissues. After validating the x-ray elastography scheme by simulation, we made a breast-mimicking phantom that contained a hard inclusion against soft background. With a micro-CT, we took 3D images of the phantom twice, changing the compressing force to the phantom. From the two 3D phantom images taken with two different compression ratios, we calculated the displacement vector maps that represented the compression-induced pixel displacements. In calculating the displacement vectors, we tracked the movements of image feature patterns from the less-compressed-phantom images to the more-compressed-phantom images using the 3D image correlation technique. We obtained strain images of the phantom by differentiating the displacement vector maps. RESULTS: The FEM simulation has shown that x-ray strain imaging is possible by tracking image feature patterns in the 3D CT images of the breast-mimicking phantom. The experimental displacement and strain images of a breast-mimicking phantom, obtained from the 3D micro-CT images taken with 0%-3% compression ratios, show behaviors similar to the FEM simulation results. The contrast and noise performance of the strain images improves as the phantom compression ratio increases. CONCLUSIONS: We have experimentally shown that we can improve x-ray strain image quality by applying 3D image correlation to the two sets of 3D CT images taken with different compression ratios. But, we need further investigations to evaluate the strain imaging performance considering the noise and decorrelation effects as well as the extra dose caused by two scans.

Analysis of time resolved femtosecond and femtosecond/picosecond coherent anti-Stokes Raman spectroscopy: application to toluene and Rhodamine 6G.

The third-order polarization for coherent anti-Stokes Raman scattering (CARS) from a pure state is described by 48 terms in perturbation theory, but only 4 terms satisfy the rotating wave approximation. They are represented by Feynman dual time-line diagrams and four-wave mixing energy level diagrams. In time-resolved (tr) fs and fs/ps CARS from the ground vibrational state, one resonant diagram, which is the typical CARS term, with three field interactions-pump, Stokes, followed by probe-on the ket is dominant. Using the separable, displaced harmonic oscillators approximation, an analytic result is obtained for the four-time correlation function in the CARS third-order polarization. Dlott's phenomenological expression for off-resonance CARS from the ground vibrational state is derived using a three-state model. We calculated the tr fs and fs/ps CARS for toluene and Rhodamine 6G (R6G), initially in the ground vibrational state, to compare with experimental results. The observed vibrational features and major peaks for both tr fs and fs/ps CARS, from off-resonance (for toluene) to resonance (for R6G) pump wavelengths, can be well reproduced by the calculations. The connections between fs/ps CARS, fs stimulated Raman spectroscopy, and impulsive stimulated scattering for toluene and R6G are discussed.

Fully converged integral cross sections of collision induced dissociation, four-center, and single exchange reactions, and accuracy of the centrifugal sudden approximation in H2 + D2 reaction.

The initial state selected time-dependent wave packet method was employed to calculate the integral cross sections for the H(2) + D(2) reaction with and without the centrifugal sudden (CS) approximation by including all important K (the projection of the total angular momentum on the body-fixed axis) blocks. With a full-dimensional model, the first fully converged coupled-channel (CC) cross sections for different competitive processes from the ground rotational state were obtained: collision induced dissociation (CID), four-center (4C) reaction and single exchange (SE) reaction. The effect of the total angular momentum J on the reaction dynamics of H(2) + D(2) and the accuracy of the CS approximation have also been studied. It was found that the CID and SE processes occur in a wide range of J values while the 4C process can only take place in a narrow window of J values. For this reason, the CC cross section for the 4C channel is merely comparable to the SE channel. A comparison of the integral cross sections from CC and CS calculations showed that the CS approximation works well for the CID process but not for the 4C and SE processes, and the discrepancy between the CC and CS cross sections grows larger as the translational energy and/or the vibrational energy increase(s).

Comparison of ring artifact removal methods using flat panel detector based CT images.

BACKGROUND: Ring artifacts are the concentric rings superimposed on the tomographic images often caused by the defective and insufficient calibrated detector elements as well as by the damaged scintillator crystals of the flat panel detector. It may be also generated by objects attenuating X-rays very differently in different projection direction. Ring artifact reduction techniques so far reported in the literature can be broadly classified into two groups. One category of the approaches is based on the sinogram processing also known as the pre-processing techniques and the other category of techniques perform processing on the 2-D reconstructed images, recognized as the post-processing techniques in the literature. The strength and weakness of these categories of approaches are yet to be explored from a common platform. METHOD: In this paper, a comparative study of the two categories of ring artifact reduction techniques basically designed for the multi-slice CT instruments is presented from a common platform. For comparison, two representative algorithms from each of the two categories are selected from the published literature. A very recently reported state-of-the-art sinogram domain ring artifact correction method that classifies the ring artifacts according to their strength and then corrects the artifacts using class adaptive correction schemes is also included in this comparative study. The first sinogram domain correction method uses a wavelet based technique to detect the corrupted pixels and then using a simple linear interpolation technique estimates the responses of the bad pixels. The second sinogram based correction method performs all the filtering operations in the transform domain, i.e., in the wavelet and Fourier domain. On the other hand, the two post-processing based correction techniques actually operate on the polar transform domain of the reconstructed CT images. The first method extracts the ring artifact template vector using a homogeneity test and then corrects the CT images by subtracting the artifact template vector from the uncorrected images. The second post-processing based correction technique performs median and mean filtering on the reconstructed images to produce the corrected images. RESULTS: The performances of the comparing algorithms have been tested by using both quantitative and perceptual measures. For quantitative analysis, two different numerical performance indices are chosen. On the other hand, different types of artifact patterns, e.g., single/band ring, artifacts from defective and mis-calibrated detector elements, rings in highly structural object and also in hard object, rings from different flat-panel detectors are analyzed to perceptually investigate the strength and weakness of the five methods. An investigation has been also carried out to compare the efficacy of these algorithms in correcting the volume images from a cone beam CT with the parameters determined from one particular slice. Finally, the capability of each correction technique in retaining the image information (e.g., small object at the iso-center) accurately in the corrected CT image has been also tested. CONCLUSIONS: The results show that the performances of the algorithms are limited and none is fully suitable for correcting different types of ring artifacts without introducing processing distortion to the image structure. To achieve the diagnostic quality of the corrected slices a combination of the two approaches (sinogram- and post-processing) can be used. Also the comparing methods are not suitable for correcting the volume images from a cone beam flat-panel detector based CT.

Inter-plane artifact suppression in tomosynthesis using 3D CT image data.

BACKGROUND: Despite its superb lateral resolution, flat-panel-detector (FPD) based tomosynthesis suffers from low contrast and inter-plane artifacts caused by incomplete cancellation of the projection components stemming from outside the focal plane. The incomplete cancellation of the projection components, mostly due to the limited scan angle in the conventional tomosynthesis scan geometry, often makes the image contrast too low to differentiate the malignant tissues from the background tissues with confidence. METHODS: In this paper, we propose a new method to suppress the inter-plane artifacts in FPD-based tomosynthesis. If 3D whole volume CT images are available before the tomosynthesis scan, the CT image data can be incorporated into the tomosynthesis image reconstruction to suppress the inter-plane artifacts, hence, improving the image contrast. In the proposed technique, the projection components stemming from outside the region-of-interest (ROI) are subtracted from the measured tomosynthesis projection data to suppress the inter-plane artifacts. The projection components stemming from outside the ROI are calculated from the 3D whole volume CT images which usually have lower lateral resolution than the tomosynthesis images. The tomosynthesis images are reconstructed from the subtracted projection data which account for the x-ray attenuation through the ROI. After verifying the proposed method by simulation, we have performed both CT scan and tomosynthesis scan on a phantom and a sacrificed rat using a FPD-based micro-CT. RESULTS: We have measured contrast-to-noise ratio (CNR) from the tomosynthesis images which is an indicator of the residual inter-plane artifacts on the focal-plane image. In both cases of the simulation and experimental imaging studies of the contrast evaluating phantom, CNRs have been significantly improved by the proposed method. In the rat imaging also, we have observed better visual contrast from the tomosynthesis images reconstructed by the proposed method. CONCLUSIONS: The proposed tomosynthesis technique can improve image contrast with aids of 3D whole volume CT images. Even though local tomosynthesis needs extra 3D CT scanning, it may find clinical applications in special situations in which extra 3D CT scan is already available or allowed.

Full-dimensional time-dependent wave packet dynamics of H2 + D2 reaction.

Collision induced dissociation (CID), four center reaction (4C), and single exchange reaction (SE) in H(2) (v(1) = high) + D(2) (v(2) = low) were studied by means of time-dependent wave packet approach within a full-dimensional model. Initial state-selected total reaction probabilities for the three competitive processes have been computed on two realistic global potential energy surfaces of Aguado-Suárez-Paniagua and Boothroyd-Martin-Keogh-Peterson (BMKP) with the total angular momentum J = 0. The role of both vibrationally excited and rotationally excited reagents was examined by varying the initial vibrational and rotational states. The vibrational excitation of the hot diatom gives an enhancement effect on the CID process, while the vibrational excitation of the cold diatom gives an inhibition effect. The rotational excitation of both reagents has a significant effect on the reaction process. The 4C and SE probabilities are at least one order of magnitude smaller than the CID probabilities over the energy range considered. Isotope substitution effects were also studied by substituting the collider D(2) by H(2) and HD on the BMKP potential energy surfaces. The CID process is most efficient for the H(2) + D(2) combination and least efficient for the H(2) + H(2) combination and is different for the 4C and SE processes.

Quantum theory of time-resolved femtosecond stimulated Raman spectroscopy: direct versus cascade processes and application to CDCl3.

We present a quantum mechanical wave packet treatment of time-resolved femtosecond stimulated Raman spectroscopy (FSRS), or two-dimensional (2D) FSRS, where a vibrational coherence is initiated with an impulsive Raman pump which is subsequently probed by FSRS. It complements the recent classical treatment by Mehlenbacher et al. [J. Chem. Phys. 131, 244512 (2009)]. In this 2D-FSRS, two processes can occur concurrently but with different intensities: a direct fifth-order process taking place on one molecule, and a cascade process comprising two third-order processes on two different molecules. The cascade process comprises a parallel and a sequential cascade. The theory is applied to the 2D-FSRS of CDCl(3) where calculations showed that: (a) the cascade process is stronger than the direct fifth-order process by one order of magnitude, (b) the sidebands assigned to C-Cl E and A(1) bends, observed on both sides of the Stokes C-D stretch frequency, are not due to anharmonic coupling between the C-D stretch and the C-Cl bends, but are instead due to the coherent anti-Stokes Raman spectroscopy (CARS) and coherent Stokes Raman spectroscopy (CSRS) fields produced in the first step of the cascade process, (c) for each delay time between the femtosecond impulsive pump and FSRS probe pulses, the line shape of the sidebands shows an inversion symmetry about the C-D stretch frequency, and this is due to the 180(∘) phase difference between the CARS and CSRS fields that produced the left and right sidebands, and (d) for each sideband, the line shape changes from positive Lorentzian to dispersive to negative Lorentzian, then to negative dispersive and back to positive Lorentzian with the period of the bending vibration, and it is correlated with the momentum of the wave packet prepared on the ground-state surface by the impulsive pump along the sideband normal coordinate.

Inverse Raman bands in ultrafast Raman loss spectroscopy.

Ultrafast Raman loss spectroscopy (URLS) is equivalent to anti-Stokes femtosecond stimulated Raman spectroscopy (FSRS), using a broadband probe pulse that extends to the blue of the narrow bandwidth Raman pump, and can be described as inverse Raman scattering (IRS). Using the Feynman dual time-line diagram, the third-order polarization for IRS with finite pulses can be written down in terms of a four-time correlation function. An analytic expression is obtained for the latter in the harmonic approximation which facilitates computation. We simulated the URLS of crystal violet (CV) for various resonance Raman pump excitation wavelengths using the IRS polarization expression with finite pulses. The calculated results agreed well with the experimental results of S. Umapathy et al., J. Chem. Phys. 133, 024505 (2010). In the limit of monochromatic Raman pump and probe pulses, we obtain the third-order susceptibility for multi-modes, and for a single mode we recover the well-known expression for the third-order susceptibility, χ(IRS) ((3)), for IRS. The latter is used to understand the mode dependent phase changes as a function of Raman pump excitation in the URLS of CV.

HF(v' = 3) forward scattering in the F + H2 reaction: shape resonance and slow-down mechanism.

Crossed molecular beam experiments and accurate quantum dynamics calculations have been carried out to address the long standing and intriguing issue of the forward scattering observed in the F + H(2) --> HF(v' = 3) + H reaction. Our study reveals that forward scattering in the reaction channel is not caused by Feshbach or dynamical resonances as in the F + H(2) --> HF(v' = 2) + H reaction. It is caused predominantly by the slow-down mechanism over the centrifugal barrier in the exit channel, with some small contribution from the shape resonance mechanism in a very small collision energy regime slightly above the HF(v' = 3) threshold. Our analysis also shows that forward scattering caused by dynamical resonances can very likely be accompanied by forward scattering in a different product vibrational state caused by a slow-down mechanism.

Probing the resonance potential in the F atom reaction with hydrogen deuteride with spectroscopic accuracy.

Reaction resonances are transiently trapped quantum states along the reaction coordinate in the transition state region of a chemical reaction that could have profound effects on the dynamics of the reaction. Obtaining an accurate reaction potential that holds these reaction resonance states and eventually modeling quantitatively the reaction resonance dynamics is still a great challenge. Up to now, the only viable way to obtain a resonance potential is through high-level ab initio calculations. Through highly accurate crossed-beam reactive scattering studies on isotope-substituted reactions, the accuracy of the resonance potential could be rigorously tested. Here we report a combined experimental and theoretical study on the resonance-mediated F + HD --> HF + D reaction at the full quantum state resolved level, to probe the resonance potential in this benchmark system. The experimental result shows that isotope substitution has a dramatic effect on the resonance picture of this important system. Theoretical analyses suggest that the full-dimensional FH(2) ground potential surface, which was believed to be accurate in describing the resonance picture of the F + H(2) reaction, is found to be insufficiently accurate in predicting quantitatively the resonance picture for the F + HD --> HF + D reaction. We constructed a global potential energy surface by using the CCSD(T) method that could predict the correct resonance peak positions as well as the dynamics for both F + H(2) --> HF + H and F + HD --> HF + D, providing an accurate resonance potential for this benchmark system with spectroscopic accuracy.