Brownian dynamics in Fourier space: membrane simulations over long length and time scales

A simulation algorithm for elastic membrane sheets is presented. Overdamped stochastic dynamics including hydrodynamic coupling to surrounding solvent and arbitrary external forces are generated by employing Fourier modes of the sheet as the primary dynamic variables. Simulations over the micron length scale and second time scale are easily achieved. The dynamics of a lipid bilayer attached to an underlying network of cytoskeletal filaments is used to estimate the diffusion constant of membrane-bound proteins on the surface of the red blood cell.     

Relaxation dynamics of Mn2+ intraion excitation in Cd0.5Mn0.5Te: Dependence on the optical pumping level

A study is reported of the Mn²⁺ intracenter 3d luminescence in a dilute Cd_0.5Mn_0.5Te magnetic semiconductor at pulsed excitations of up to 3.5 MW/cm². At high excitation levels and at a temperature of 77 K, the kinetics varies strongly over the emission band profile. The luminescence decay curve can be resolved into a fast and a delayed component, which correspond to the excitation of extended and localized states in the manganese ion system. The fast relaxation of the extended states is largely determined by the up-conversion. As the temperature is lowered, the contribution of the fast component at the center of the emission band and in its low-energy wing decreases because of the weakening role of the extended states lying above the mobility edge.     

High resolution Fourier transform spectrum of HDO in the 7500-8200 cm region: revisited

The HDO absorption FT spectrum is recorded and analyzed in the 7500-8200 cm⁻¹ spectral region. The high accuracy ab initio calculation of Schwenke and Partridge was successfully applied for spectrum assignment that resulted in derivation of 508 precise rovibrational energy levels for the (3 0 0), (0 3 1), (1 1 1), (0 6 0), (2 2 0), and (0 0 2) states, with 295 of them being reported for the first time. In particular, eight new energy levels, including the band center at 7914.3170 cm⁻¹, were derived for the highly excited bending (0 6 0) state from transitions borrowing their intensities through local high-order resonance coupling with the (3 0 0) and (0 3 1) states.     

Complex local dynamics in DNA on the picosecond and nanosecond time scales

Time-resolved Stokes shift measurements of the local structural relaxation of three DNA oligonucleotides are presented. Logarithmic relaxation is seen for over three decades in time (40 ps-40 ns), indicating a complex relaxation among a large number of conformational substates. The observed relaxation is the same in all the sequences. Sequence dependence of the localized dynamics of DNA does not appear within this time range. We infer that 30%-50% of the relaxation is faster than 40 ps, has a nonlogarithmic decay and has a sequence dependent amplitude.     

Analysis of the Fourier transform spectrum of 13C18O2 in the 4.3- and 16-μm regions

Fourier transform spectra have been obtained for ¹³C¹⁸O₂ in the regions of ν₂ (16 μm) and ν₃ (4.3 μm) at a resolution of 0.04 cm^?1. From a least-squares fit of the P- and R-branch lines for the transitions, values have been calculated for the rotational constants B, the centrifugal distortion constants D, and the band origins. Based on the derived constants, the calculated wavenumbers for the P and R lines of both the 01¹0-00⁰0 and 00⁰1-00⁰0 transitions agree with the observed positions within ±0.003 cm^?1. We have also observed the difference bands ν₁-ν₂ and the hot bands (ν₃ + ν₂) ? ν₂. From an analysis of these transitions we have determined values for the l-doubling constants for ν₂ and the location of the inactive fundamental ν₁.     

激光单稳频指标的激光计量红外光谱仪精度分析

在傅里叶变换红外光谱仪中,采用激光计量光程差可提高光谱的测量精度。激光波长作为光程差测量的基准单位,其线宽和稳频特性直接决定了光程差的误差,进而影响光谱的测量精度。根据光谱仪的干涉原理,通过傅里叶逆变换和误差分析方法,建立了光谱测量相对误差与激光单稳频指标之间的理论模型,并对该模型进行了仿真计算。结果证明,该模型可作为设计激光计量光程差光谱仪系统的理论依据。     

Effect of the nonlinearity of the CCD in Fourier transform profilometry on spectrum overlapping and measurement accuracy

In Fourier transform profilometry (FTP), we must restrain spectrum overlapping caused by the nonlinearity of the charge coupled device (CCD) and increase the measurement accuracy of the object shape. Firstly, the causes of producing higher-order spectrum components and inducing spectrum overlapping are analysed theoretically, and a simple physical explanation and analytical deduction are given. Secondly, aiming to suppress spectrum overlapping and improve measurement accuracy, the influence of spatial carrier frequency of projection grating on them is analysed. A method of increasing the spatial carrier frequency of projection grating to restrain or reduce the spectrum overlapping significantly is proposed. We then analyze the mechanism of how the spectrum overlapping is reduced. Finally, the simulation results and experimental measurements verify the correction of the proposed theory and method.     

High-resolution Fourier transform spectrum of H2S in the region of 8500-8900 cm

High-resolution Fourier transform infrared spectrum of H₂S was recorded and analyzed in the region of the polyad. More than 450 transitions were assigned to the 3ν₁ + ν₂ and 2ν₁ + ν₂ + ν₃ bands with the maximum values of quantum numbers J and K_a equal to 14, 7, and 14, 9 for these two bands, respectively. The theoretical analysis was fulfilled with the Hamiltonian which takes into account strong resonance interactions among the studied vibrational states (3 1 0), (2 1 1), and also “dark” states (0 3 2) and (2 3 0). The rms deviation is 0.0019 cm⁻¹. The intensity borrowing effect in the doublets in the P-branch transitions of the 3ν₁ + ν₂ and 2ν₁ + ν₂ + ν₃ bands is observed and discussed.     

Analysis of the microwave rotation spectrum of silyl cyanide,SiH3CN,in its ground and vibrationally excited states

The rotational spectrum of silyl cyanide, SiH₃CN, has been studied by microwave spectroscopy. A detailed analysis of the transitions in the excited states of the ν₃, ν₄, ν₇, and ν₈ modes has been carried out. In particular the v₈ = 1, 2, 3, and 4 vibrational satellites have been subjected to a complete vibration-rotation analysis. Ground state transitions of ²⁸SiH₃¹²C¹⁴N, ²⁹SiH₃¹²C¹⁴N, ³⁰SiH₃¹²C¹⁴N, ²⁸SiH₃¹³C¹⁴N, and ²⁸SiH₃¹²C¹⁵N have all been studied in natural abundance. The overall study has yielded a large amount of detailed vibration-rotation data. The effects of quadrupole interactions have been taken into account. To confirm the analysis, computer simulated spectra have been compared with those observed.     

Femtosecond to nanosecond relaxation time scales in electronically excited tetrakis(dimethylamino)ethylene: identification of the intermediates

In the TDMAE molecule (title molecule), the time evolution has been analyzed from the very initial excitation step down to a fluorescent state, over widely different time scales. Pump probe measurements have been performed at 3 different excitation wavelengths 400, 266 and 200 nm. The decay has been followed over the femtosecond and subnanosecond ranges with this method and the decay of the final charge transfer state has been detected by its fluorescence emission. This allows an overview of the complete decay mechanism. The initial relaxation pathway is interpreted in a similar way to ethylenic molecules, where the initial wavepacket is quickly trapped in a doubly excited state Z with charge transfer character. Then the Z state decays slowly (10-100 picoseconds) into the final state. In difference to monoalkenes the final stage of this evolution is a charge transfer state. The decay of transient Z state to the charge transfer state is a further assessment of the partial ionic character of the Z state. This type of molecule with low ionization potential can be viewed as a demonstrative example of the interrelation between the charge induced forces and the deformations in excited state reaction dynamics. Received 17 January 2001 and Received in final form 23 February 2001     

Fourier transform spectroscopy of the low-lying excited electronic states of FeO: A new perturbing Σ state and improved ground state constants

A small rotational perturbation has been found in the ⁵Δ_i ground state of FeO. This occurs in the v = 2 level of the $\text{Ω}\text{= 2}$ substate, and only one Λ-boudling component of one rotational level is affected. The perturbing state, which lies about 2100 cm^?1 above the lowest spin-orbit level of the molecule, is orbitally nondegenerate, and is likely to belong to the ⁷Σ⁺ state arising from the configuration (4sσ)¹(3dδ)²(3dπ)²(3dσ)¹. The new state, a⁷Σ⁺, is possibly responsible for anomalies in the intensity pattern of the FeO^? photodetachment spectrum of Engelking and Lineberger [J. Chem. Phys., 66, 5054–5058 (1977)]. Improved vibrational and rotational constants are presented for the ground state, combining new Fourier transform measurements of the Λ-doubling in X⁵Δ₁ with the recent microwave data of Endo et al. [Astrophys. J., 278, L131–132 (1984)].     

Study of femtosecond dynamics in vibrationally excited free bis(trifluoromethyl)ketene and metal carbonyl molecules induced by CO bond resonant excitation

The dynamics of relaxation processes in free bis(trifluoromethyl)ketene (CF₃)₂CCO and Fe(CO)₅ and Cr(CO)₆ metal carbonyl molecules after multiphonon excitation of the C=C=O and C=O vibrations by femtosecond laser infrared radiation was studied. The temporal and spectral dependences of the relaxation of the excited vibrational states were measured. Kinetics with a characteristic decay time of about 5 ps was obtained for (CF₃)₂CCO molecules. Its behavior is interpreted as a manifestation of the intramolecular relaxation of the excited vibration states of the resonance mode. Kinetic curves with characteristic times of about 250–500 fs were observed for Fe(CO)₅ and Cr(CO)₆. The behavior of these curves depends on the mutual orientation of the polarizations of the pump and probe pulses.     

Studies of the mid- and far-infrared laser magnetic resonance spectra of the CD radical: information on vibrationally excited levels

Two separate studies of the CD radical in vibrationally excited levels of its X²Π ground state have been made by the technique of laser magnetic resonance. The first of these studies was in the far-infrared; rotational transitions of CD in the v=1 and 2 levels have been detected. The second study was carried out in the mid-infrared using a carbon monoxide laser magnetic resonance spectrometer. In these experiments, transitions in the (1,0), (2,1), and (3,2) bands have been detected. All the available data on CD in its X²Π state have been used to determine an improved set of molecular parameters for the CD radical. In addition to the above data sets, previous far-infrared laser magnetic resonance on the CD radical in the v=0 level and FTIR observations of the (1,0) and (2,1) bands have been included. The principal molecular parameters determined are: , , , , where the figures given in parentheses are one standard deviation from the least squares fit. A small but significant dependence of the orbital contribution to the magnetic dipole moment on the vibrational quantum number is detected. This may reflect the mixing between the X²Π and a⁴Σ^- states of CD.     

Sn and Sn hyperfine structure in the rotational spectrum of tin monosulfide recorded using laser ablation-source equipped, chirped-pulse Fourier transform microwave spectroscopy

Tin metal has been ablated with pulsed radiation from a Nd:YAG laser (λ=1064 nm). Carbonyl sulfide, diluted in high pressure argon, has been pulsed into the resultant Sn plasma. One of the results of this experiment has been the production of SnS. These events have allowed a rotational spectrum of tin monosulfide to be studied using a chirped-pulse Fourier transform microwave spectrometer. The resolution of the spectrum obtained was sufficient to observe hyperfine structure from the ¹¹⁷Sn and ¹¹⁹Sn-containing SnS molecules. Tin nuclear spin-rotation hyperfine constants are reported for the first time.     

Fourier transform infrared studies of cyclohexane and benzene adsorbed on Pt/Al2O3: Evidence for π- and σ-bonded chemisorbed species

Fourier transform infrared spectroscopy has been applied to the study of cyclohexane adsorbed on Al₂O₃ and Pt/Al₂O₃ surfaces. Earlier studies of benzene on these same materials have also been extended to include benzene adsorbed on a Pt/Al₂O₃ surface which contains structured carbon residues. The data provide indirect evidence for the formation of a carbon residue on Pt/Al₂O₃ which retains the six-membered cyclic structure of the parent adsorbates. The carbon residue can be formed upon vacuum heating of the parent C₆ ring molecules chemiorbed on Pt/Al₂O₃. There is spectroscopic evidence that cyclohexane dehydrogenates on Pt/Al₂O₃ at 300 K to form two different chemisorbed species; a π-bonded benzene and a dissociated σ-bonded benzene. These two chemisorbed species have CH stretching vibrations centered at 3030 and 2947 cm^?1, respectively. Benzene added to a clean catalyst surface forms only a π-bonded benzene. However, benzene added to Pt/Al₂O₃ with ordered carbon residues forms both π- and σ-bonded benzenes. The addition of H₂ at 300 K to any of the π- or σ-bonded benzenes or to the carbon residue results in the formation of cyclohexane physisorbed on the catalyst. The absence of CH₃ groups upon hydrogenation suggests the lack of CC bond breaking during adsorption or hydrogenation. Simultaneous infrared and thermal desorption studies on chemisorbed deuterated benzene (from C₆D₁₂) indicate that the a-bonded species exchange H from the surface OH groups of the alumina support more readily than does the π-bonded benzene. In addition to hydrogen exchange with the support, thermal desorption experiments indicate the oxidation of a portion of the chemisorbed hydrocarbons and/or carbon residue by oxygen from the alumina support. Therefore, the support is capable of playing a direct role in reactions occurring on the catalyst surface.     

Microwave spectrum of methyl fluoride in excited vibrational states: Coriolis interaction and anomalous l-doubling transitions

The microwave spectrum of CD₃F in the v₂ = 1, v₃ = 1, v₅ = 1, and v₆ = 1 states was observed, including the direct l-doubling transitions in the v₅ = 1 and v₆ = 1 states. The Coriolis interaction between the v₂ = 1 and v₅ = 1 states was analyzed in detail. An anomaly in the Stark effect was noticed in some of the direct l-doubling transitions in the v₆ = 1 states, and was explained in terms of accidental degeneracy between the Kl₅ = 1 and the Kl₅ = ? 2 levels. Molecular constants associated with the vibrational and rotational motions were determined through an analysis of these spectra.The J = 1 ← 0 transitions of ¹²CH₃F in the v₂ = 1, v₃ = 1, v₅ = 1, and v₆ = 1 states and of ¹³CH₃F in the v₃ = 1 and v₆ = 1 states were observed, as well as the direct l-doubling transitions of ¹²CH₃F in the v₅ = 1 state. A preliminary analysis was carried out on the strong Coriolis interaction between the v₂ = 1 and v₅ = 1 states.     

基于小波变换的体内外酒精含量近红外光谱检测与分析

应用小波分析对体外和体内的酒精近红外光谱信号进行去噪分析,通过体外光谱分析确定酒精吸收峰特征范围,为体内近红外光谱分析确定有效区间。软阈值和硬阈值下,分别采用缺省阈值、Birge-Massart阈值和最大最小值阈值,比较酒精光谱去噪,信噪比(signal noise ratio,SNR)和均方根误差(root mean square error,RMSE)去噪效果。结果表明:缺省硬阈值方法对酒精近红外光谱去噪的效果较好;小波变换可以有效去除酒精近红外光谱的噪声,提高信噪比,保留有用真实信号。在不同的酒精浓度下,去噪后的近红外光谱能够较好的显示浓度变化规律。小波分析在近红外光谱法对人体酒精无创检测及定量分析方面有较好的应用前景。     

Fourier transform spectroscopy of CO2 and OCO in the 3800-8500 cm region and the global modeling of the absorption spectrum of CO2

The absorption spectrum of the ¹⁸O enriched carbon dioxide has been recorded at Doppler limited resolution with a Fourier transform spectrometer in the spectral range 3800-8500 cm⁻¹. Seventeen cold bands (14Σ-Σ and 3Σ-Π) and nine hot bands (9Π-Π) of ¹²C¹⁸O₂, nineteen cold bands (18Σ-Σ and 1Σ-Π) and eighteen hot bands (6Σ-Σ, 9Π-Π and 3Δ-Δ) of ¹⁶O¹²C¹⁸O have been observed. Among them, 14 ¹²C¹⁸O₂ bands and 12 ¹⁶O¹²C¹⁸O bands are observed for the first time. The spectroscopic parameters G_v, B_v, and centrifugal distortion constants, have been determined for all observed bands. Effective Hamiltonian parameters for the ¹²C¹⁸O₂ isotopic species are retrieved from the global fitting of the observed line positions presented in this paper and collected from the literature. As the result, 65 obtained effective Hamiltonian parameters reproduce 5443 observed line positions of 73 ¹²C¹⁸O₂ bands with RMS = 0.00145 cm⁻¹.