Doppler Profiles Research Articles

ChemInform Abstract: Photodissociation of Methyl Hydroperoxide at 266 nm: Vector Correlations and Energy Distribution in the OH Fragment.

The energy content and correlation of vectorial properties of the OH fragment photoejected by methyl hydroperoxide (CH3OOH) at 266 nm are probed by laser excitation, polarization, and high‐resolution sub‐Doppler spectroscopy. The nascent OH is found to be vibrationally cold and the rotational distribution peaks at ∼N=6. Polarization dependence of the fragment Doppler profiles and nonequilibrium Λ‐doublet populations show that, at high rotational energy, the velocity vector of the OH fragment has a preference to be perpendicular to the planes of rotation of the nuclei and the half‐filled 2pπ orbital. The fragment angular distribution indicates that dissociation of the parent excited state is fairly prompt, with a lifetime of ∼250 fs.

ChemInform Abstract: Fine Structure Branching Ratios and Doppler Spectroscopy of Chlorine Atoms from the Photodissociation of Alkyl Chlorides and Chlorofluoromethanes at 157 and 193 nm.

Alkyl chlorides (R=CH3, C2H5, C3H7, and C4H9), chloromethanes (CHnCl4−n), and chlorofluoromethanes (CFnCl4–n) are photodissociated at 157 and 193 nm. The chlorine atom photofragments are detected by a resonance enhanced multiphoton ionization technique. The branching ratios of the Cl photofragments [Cl*(3p2P1/2)]/[Cl(3p2P3/2)] are almost identical (0.23±0.03) for alkyl monochlorides at 157 and 193 nm and for CH2Cl2 and CHCl3 at 157 nm, while the ratios are rather small (0.10±0.02) for CH2Cl2 and CHCl3 at 193 nm. No discernible isotope effects on the branching ratios were observed when D atoms were substituted for H atoms in chloromethanes. For CCl4, CF3Cl, CF2Cl2, CFCl3 at 157 and 193 nm, the ratios are small (<0.05) irrespective of the number of Cl atoms in the parent molecules. The Doppler profiles of the chlorine photofragments have been obtained and it is found that (a) CF3Cl undergoes a perpendicular optical transition at 157 nm and (b) for halomethanes containing more than two Cl atoms, the Cl photo...

Volterra equation for the matrix source function at resonance scattering

A matrix transfer equation for multiple resonance scattering of radiation in a spectral line in a semiinfinite atmosphere with a uniform distribution of primary radiation sources is examined. A nonlinear matrix integral is obtained for this equation as a generalization of the Rybicki two-point Q-integral. One special case of the matrix $ {\mathbf{\hat{Q}}} $ -integral is the Volterra equation for the matrix source function of the problem discussed here. The Volterra equation is solved numerically for a Doppler profile of the absorption coefficient. Several polarization characteristics of the emerging radiation are obtained.

Doppler effect in fragment autoionization following core-to-Rydberg excitations of N2

The autoionization of atomic fragments after core-to-Rydberg excitations in N2 has been studied using high-resolution electron spectroscopy. Doppler profiles are clearly observed on atomic autoionization peaks and show dependence on the symmetries of the excited states. It is demonstrated that information on the femtosecond dissociation dynamics after the Rydberg excitations can be gained through an analysis of the Doppler profiles.

Min-norm method for estimating delay and Doppler profiles from FMCW channel data with in-band interference

The min-norm (MN) method is shown to improve estimates of delay profile and Doppler spectrum from frequency modulated continuous-wave (FMCW) channel data corrupted with in-band interference. Results of MN estimates are examined by comparing with those obtained from FFT processing.

Heritability and Genetic Linkage of Left Ventricular Mass, Systolic and Diastolic Function in Hypertensive African Americans (From the GENOA Study)

Much of the interindividual variation in left ventricular (LV) structure and function is unexplained by established risk factors and may be due to novel or genetic factors. We used pedigree information from 454 tandem markers across the genome to estimate the heritability and linkage of various echocardiographic measures of LV structure and function in a cohort of African-American hypertensive siblings. LV mass was calculated according to the American Society of Echocardiography (ASE) simplified cubed equation and indexed to height(2.7). Fractional shortening (FS) was calculated as the percent change in the internal diameter between diastole and systole. Ejection fraction (EF) was calculated from ventricular diameters. Peak mitral early and late diastolic filling velocities were measured from the transmitral pulsed Doppler profile. The maximum-likelihood heritability estimate for each phenotype was obtained using a variance components method. Linkage analyses were performed using the multipoint variance components-based approach. There was moderate heritability for LV mass index (34%), interventricular septal thickness (29%), diastolic diameter (42%), EF (40%), FS (39%), and mitral early and late diastolic filling velocities (37 and 45%, respectively). The greatest evidence of genetic linkage was observed for LV mass index on chromosome 3 (logarithm of odds (LOD) score = 2.38), LV EF on chromosome 12 (LOD score = 2.39), and mitral E-wave velocity (MVE) on chromosome 19 (LOD score = 2.69). In this African-American cohort of hypertensive siblings, the greatest evidence for linkage of LV structure and function was on chromosomes 3, 12, and 19.

Frequency modulated circular dichroism spectroscopy: application to ICN photolysis

CN photofragments produced in the 248 nm photolysis of ICN are characterised by frequency-modulated absorption spectroscopy in the red A2Π ← X2Σ+ system. A range of high rotational states in both v = 0 and v = 1 were selected to isolate only those dissociation channels including coincident ground state I(2P3/2). Velocity-resolved alignment and orientation parameters are determined from the observed Doppler profiles. The alignment measurements for both v = 0 and v = 1 levels are very similar, and consistent with dissociation occurring via three distinct pathways, beginning with simultaneous excitation of the 4A′(3Π0+), 5A′(1Π1) and 5A″(1Π1) surfaces. While the incoherent alignment parameters for both v = 0 and v = 1 products are similar, the corresponding coherent orientation parameters are markedly different. CN (v = 0, N) exhibits a large positive orientation, whereas all rotational states probed in v = 1 show a much smaller orientation. This is consistent with the previously observed change in the sign of the coherent orientation parameter between v = 0 and v = 2.

Plasma Temperature Determination of Hydrogen Containing High-Frequency Electrodeless Lamps by Intensity Distribution Measurements of Hydrogen Molecular Band

The goal of the present work was the investigation of the possibility to use intensity distribution of the Q-branch lines of the hydrogen Fulcher-α diagonal band (d3Πu−→a3∑g+ electronic transition; Q-branch with v=v′=2) to determine the temperature of hydrogen containing high-frequency electrodeless lamps (HFEDLs). The values of the rotational temperatures have been obtained from the relative intensity distributions for hydrogen-helium and hydrogen-argon HFEDLs depending on the applied current. The results have been compared with the method of temperature derivation from Doppler profiles of He 667.8 nm and Ar 772.4 nm lines. The results of both methods are in good agreement, showing that the method of gas temperature determination from the intensity distribution in the hydrogen Fulcher-α (2-2)Q band can be used for the hydrogen containing HFEDLs. It was observed that the admixture of 10% hydrogen in the argon HFEDLs significantly reduces the gas temperature.

Ion velocity filter effect observed in dayside hydrogen aurora

Observations of dayside auroral hydrogen emissions of Hα (λ656.3 nm) were carried out using spectrometers on Svalbard at Ny‐Ålesund (NYA: 76.3°N, 111.0°E CGM) and Longyearbyen (LYR: 75.3°N, 111.9°E CGM). Using a Monte Carlo model, simulated Doppler profiles were fitted to the spectra to estimate precipitating proton energy. A difference in energy was found between the sites for approximately 45 minutes. When combined with measurements of antisunward convection, the energies are consistent with the inverse variation of ion energy with latitude observed by satellites in the cusp region, known as the ion velocity filter. This is the first measurement of the ion velocity filter effect in the dayside aurora using ground‐based optical instrumentation. The increasing difference in energy observed is interpreted as a measure of the decreasing merging rate at the magnetopause.

Analysis and extraction of stepped frequency radar signature for micro-motion structure

Radar signature produced by micro-motion structures contains movement and structure information which is useful for radar target recognition. For stepped frequency (SF) radar, the Doppler modulation is coupled with the stepped carrier frequency. It shifts and smears the high-resolution range profile and makes it difficult to analyse and extract the micro-motion information from the range profile directly. The authors propose to comprehend the SF radar as a special pulse Doppler radar, and the range profile as a Doppler profile for the convenience of motion analysis. The signature of moving targets for SF radar is analysed from this point of view and the equivalent instantaneous Doppler frequency (EIDF) is introduced. Then, a typical micro-motion, rotation, is taken as an example. The sinusoidal vibration of the peaks in the range profile sequence is explained in detail, especially the relationship between the sinusoid parameters and the rotation parameters. An approach to extract the rotation parameters from the range profile or EIDF spectrum sequence is proposed based on the Hough transform. Simulated and experimental results validate the theoretical analysis and the feature extraction method.

Analysis of High Efficiency Electromagnetically Induced Transparency in Potassium Vapor

We present a rate-equation theoretical model describing the optical pumping processes on the K D1 line and we then discuss their influence on the electromagnetically induced transparency resonance parameters. We present also a comparison with the results of an experiment performed in cells containing pure alkali metal or added with a few torrs of buffer gas. The model shows that, in the last case, the complete Maxwellisation of the atomic population velocity distribution, along with the overlapping Doppler profiles of the transitions from the ground-states typical of K, leads to a partial compensation of optical pumping and a significant increase of the amplitude of the electromagnetically induced transparency resonances.

A comparative study of hydrogen-atom release dynamics in radical–radical reactions

This paper presents a comparative study of the atomic hydrogen release dynamics in the oxidation reactions of saturated and unsaturated hydrocarbon radicals. The prototypal radical–radical reactive scattering processes were examined by applying a combination of crossed beams and high-resolution vacuum-ultraviolet laser-induced fluorescence spectroscopy. With the aid of ab initio and statistical calculations, remarkable dynamic features were uncovered in the Doppler profile analysis of the atomic hydrogen products. The difference in the reactivity of saturated and unsaturated hydrocarbon radicals could be rationalized in terms of the characteristic geometry of the transition state and activation barriers along the exit channel on the doublet potential energy surface.

Crossed-beam intermodulated fluorescence spectroscopy as a spatially resolved temperature diagnostic for supersonic nozzles

A variant of laser saturation spectroscopy has been applied to the determination of spatially resolved temperature in low-pressure supersonic flows. By copropagating a pump and probe beam with a small crossing angle, the full Doppler profile is retained, but the signal is limited to the volume where both beams are overlapped. The technique was demonstrated on several rovibrational lines of the I2X1Sigma(0g+)-->B3Pi(0u+) transition in a Mach 2 Laval nozzle. A temperature of 146 K+/-1.5 K was extracted from measurements of the I2P(46) 17-1 spectral line with a spatial resolution of 2.4 mm3. Application of the technique to the turbulent gain medium of a chemical oxygen-iodine laser is discussed.

Analysis of electromagnetically induced transparency and slow light in a hot vapor of atoms undergoing collisions

We present a realistic theoretical treatment of a three-level $\Lambda$ system in a hot atomic vapor interacting with a coupling and a probe field of arbitrary strengths, leading to electromagnetically-induced transparency and slow light under the two-photon resonance condition. We take into account all the relevant decoherence processes including col5Blisions. Velocity-changing collisions (VCCs) are modeled in the strong collision limit effectively, which helps in achieving optical pumping by the coupling beam across the entire Doppler profile. The steady-state expressions for the atomic density-matrix elements are numerically evaluated to yield the experimentally measured response characteristics. The predictions, taking into account a dynamic rate of influx of atoms in the two lower levels of the $\Lambda$, are in excellent agreement with the reported experimental results for $^4$He*. The role played by the VCC parameter is seen to be distinct from that by the transit time or Raman coherence decay rate.

Energetic ion, atom, and molecule reactions and excitation in low-currentH2discharges: Model

Models of the elastic, inelastic, and reactive collisions of energetic hydrogen ions, atoms, and molecules are developed for predicting H_{alpha} and H2 near-uv emission, H_{alpha} Doppler profiles, and ion energy distributions for low-pressure, low-current discharges in H2 . The model is applied to spatially uniform electric field E to gas density N ratios of 350 Td< or =E/N< or =45 kTd and 8 x10;{19}< or =Nd< or =10 x10;{21} m;{-2} , where d is the electrode separation and 1 Td=10;{-21} V m;{2} . Mean ion energies at the cathode are 5-1500 eV. Cross sections for H+ , H2+ , H3+ , H, H2 , and excited H(n=3) collisions with H2 and reflection probabilities from electrodes are updated and summarized. Spatial and energy distributions of ions and fast neutrals are calculated using a "multibeam" technique. At the lower E/N and Nd , electron excitation of H_{alpha} dominates near the anode. Excitation of H_{alpha} by fast H atoms near the cathode increases rapidly with pressure through a multistep reaction sequence. At higher E/N , fast H atoms produced at the cathode surface excite much of the H_{alpha} . The model agrees with experimental spatial distributions of H_{alpha} emission and Doppler profiles. Ion energy distributions agree with experiments only for H2+ . Cross sections are derived for excitation of the near-uv continuum of H2 by H atoms.

Nonlinear magneto-optical resonances atD1excitation ofR85bandR87bfor partially resolved hyperfineFlevels

Experimental signals of non-linear magneto-optical resonances at D1 excitation of natural rubidium in a vapor cell have been obtained and described with experimental accuracy by a detailed theoretical model based on the optical Bloch equations. The D1 transition of rubidium is a challenging system to analyze theoretically because it contains transitions that are only partially resolved under Doppler broadening. The theoretical model took into account all nearby transitions, the coherence properties of the exciting laser radiation, and the mixing of magnetic sublevels in an external magnetic field and also included averaging over the Doppler profile. Great care was taken to obtain accurate experimental signals and avoid systematic errors. The experimental signals were reproduced very well at each hyperfine transition and over a wide range of laser power densities, beam diameters, and laser detunings from the exact transition frequency. The bright resonance expected at the F_g=1 --> F_e=2 transition of Rb-87 has been observed. A bright resonance was observed at the F_g=2 --> F_e=3 transition of Rb-85, but displaced from the exact position of the transition due to the influence of the nearby F_g=2 --> F_e=2 transition, which is a dark resonance whose contrast is almost two orders of magnitude larger than the contrast of the bright resonance at the F_g=2 --> F_e=3 transition. Even in this very delicate situation, the theoretical model described in detail the experimental signals at different laser detunings.

Site-dependent photodissociation of vibrationally excited CD3NH2

The N-H and C-D bond fission in partially deuterated methylamine, CD(3)NH(2), has been investigated using vibrationally mediated photodissociation. Jet-cooled action spectra and Doppler profiles of the H and D photofragments were monitored following approximately 243.1 nm photodissociation of the parent pre-excited to two, three or four N-H stretch quanta. The action spectra were analyzed in terms of simplified local mode/normal mode (LM/NM) and NM models, allowing band assignment and determination of the strong resonances involved in the coupling. The Doppler profiles show that the released H and D photofragments have low translational energy content and that the H is the dominant product, although its yield decreases as higher pre-excited N-H vibrational states are dissociated. The dynamics of the site-dependent bond fission in CD(3)NH(2) is discussed.

Coherent population trapping and strong electromagnetically induced transparency resonances on the D1 line of potassium

In this paper we report the first experimental observation of coherent population trapping (CPT) in thermal potassium vapor in a three levels Λ scheme. We demonstrate that K presents the advantage of a reduced modulation frequency with a large resonance contrast (up to 40%), in comparison to similar approaches with other alkalis. We report also the first evidence of electromagnetically induced transparency (EIT) resonances in K in the so called Hanle configuration. We tested different kinds of cells, demonstrating strong enhancement of the resonance contrast and amplitude for antirelaxation coated and buffered cells containing K vapor: resonance contrast up to 90% (for coated cells) and 65% (for buffered cells) is achieved with a linewidth of about 13 mG, while under similar conditions, the EIT resonance contrast in Cs vapor buffered by Ar gas is about 1%. Such relevant improvement is due to the reduced optical pumping in K, because of the overlapping of the hyperfine levels Doppler profiles, which does not occur in the case of Rb and Cs vapor. For this reason, K can be considered very promising for further CPT and EIT applications, especially for those where optical pumping losses represent a major limiting factor, such as light slowing and magnetometry.

Cabrol Composite Graft for Aortic Root Replacement: Echocardiographic Imaging

A 55-yr-old woman with history of Marfan syndrome presented with an enlarging aortic arch aneurysm. Fifteen years ago, she had undergone repair of an aortic root aneurysm. A preoperative transthoracic echocardiogram (TTE) revealed normal biventricular function, 3+ tricuspid regurgitation, a small nonobstructive mechanical aortic prosthesis, and an aortic root graft. The distal ascending aorta and aortic arch were dilated, measuring 5 cm in diameter. Left heart catheterization showed normal coronary arteries originating from the aortic root graft, with the left adjacent to the right. The patient was scheduled for aortic arch reconstruction and tricuspid valve repair.

Diode laser based studies of the UV photolysis of molecular iodine

The photolysis of molecular iodine at 193 and 248 nm has been studied by diode laser based frequency-modulated (FM) absorption spectroscopy with detection of the nascent iodine photofragment via the I((2)P(1/2)-(2)P(3/2)) transition at 1.315 microm. Use of narrow band radiation enables nascent measurements with sufficient speed resolution to allow both the character of the initial electronic transition and speed of the fragments to be determined. The time dependence of the integrated area of the measured Doppler profiles has been used to determine both the I* quantum yield and the collisional electronic quenching rate constant of I* (I* = (2)P(1/2)) by I(2). These values are also determined using the diode laser gain versus absorption technique. In the 248 nm case an I* quantum yield of 0.45 +/- 0.04 and 0.42 +/- 0.04 is found by each method, respectively, and an electronic quenching rate constant of (3.6 +/- 0.5) x 10(-11) cm(3) molecule(-1) s(-1), consistent with literature, is determined. The form of the nascent Doppler profile indicates that excitation to a Omega = 1 state dominates, with subsequent dissociation to I((2)P(1/2)) + I((2)P(3/2)), in keeping with assignment of the upper state as 1441 (3)Sigma(+)(1(u)). The deviation from Phi(I*) = 0.5 can be attributed to a contribution from the 1441 (3)Sigma(+)(0(u)(-)) state which dissociates to two ground state iodine atoms. 193 nm excitation exhibits more complicated dynamics and kinetics, including a pressure dependent I* quantum yield. At the low pressures, <200 mTorr, used in the FM Doppler measurements there are two speed components to the profile suggesting multiple dissociation pathways. Firstly, fast iodine fragments indicate single photon absorption in a parallel transition followed by direct dissociation. Secondly, a slower speed component can be attributed to iodine atoms formed after radiative transfer to unbound levels in the ground state and the a' surface. Investigation of the changes in Doppler profiles with time suggest that some of the a' surface population may transfer to the bound B((3)Pi(0u)(+)) state which then in turn undergoes collision-induced predissociation to produce I atoms on the ground electronic state.