Barrier to internal rotation, symmetry and carbonyl reactivity in methyl 3,3,3-trifluoropyruvate

AbstractHigh-resolution rotational spectroscopy was used to investigate the conformational landscape of methyl-3,3,3-trifluoropyruvate, a small, partially-fluorinated molecule, which is of interest because of its chemical properties and reactivity in contrast to the unfluorinated species. Methyl 3,3,3-trifluoropyruvate is also subject to two possible large amplitude motions of the methyl and trifluoromethyl group. However, only the methyl rotor gives rise to the tunneling splitting specific to individual conformers. In the rotational spectrum measured in the frequency region from 6 to 27 GHz, the identified conformers, s-cis and s-trans, were fitted to experimental accuracy, resulting in the accurate determination of the vibrational ground state rotational constants ${A}_{0}=2185.05827\left(36\right)\text{\hspace{0.17em}MHz}$, ${B}_{0}=1023.30031\left(17\right)\text{\hspace{0.17em}MHz}$, and ${C}_{0}=803.520287\left(95\right)\text{\hspace{0.17em}MHz}$ for the s-cis conformer, and ${A}_{0}=2706.9024\left(49\right)\text{\hspace{0.17em}MHz}$, ${B}_{0}=864.889539\left(81\right)\text{\hspace{0.17em}MHz}$, and ${C}_{0}=746.532896\left(71\right)\text{\hspace{0.17em}MHz}$ for the s-trans conformer. Additionally the barrier heights of the methyl rotor ${V}_{3}\left({\text{CH}}_{3}\right)=363.116\left(94\right){\text{\hspace{0.17em}cm}}^{-1}$ and ${V}_{3}\left({\text{CH}}_{3}\right)=389.290\left(80\right){\text{\hspace{0.17em}cm}}^{-1}$ were obtained for the s-cis and s-trans conformer, respectively.

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Broad-band high-resolution rotational spectroscopy for laboratory astrophysics

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935197 ◽

2019 ◽

Vol 626 ◽

pp. A34 ◽

Cited By ~ 6

Author(s):

J. Cernicharo ◽

J. D. Gallego ◽

J. A. López-Pérez ◽

F. Tercero ◽

I. Tanarro ◽

...

Keyword(s):

Spectral Resolution ◽

Accurate Determination ◽

Broad Band ◽

Laboratory Astrophysics ◽

High Spectral Resolution ◽

Rotational Spectroscopy ◽

Rotational Spectrum ◽

Vibrationally Excited ◽

Radio Receivers ◽

Cold Plasmas

We present a new experimental set-up devoted to the study of gas phase molecules and processes using broad-band high spectral resolution rotational spectroscopy. A reactor chamber is equipped with radio receivers similar to those used by radio astronomers to search for molecular emission in space. The whole range of the Q (31.5–50 GHz) and W bands (72–116.5 GHz) is available for rotational spectroscopy observations. The receivers are equipped with 16 × 2.5 GHz fast Fourier transform spectrometers with a spectral resolution of 38.14 kHz allowing the simultaneous observation of the complete Q band and one-third of the W band. The whole W band can be observed in three settings in which the Q band is always observed. Species such as CH3CN, OCS, and SO2 are detected, together with many of their isotopologues and vibrationally excited states, in very short observing times. The system permits automatic overnight observations, and integration times as long as 2.4 × 105 s have been reached. The chamber is equipped with a radiofrequency source to produce cold plasmas, and with four ultraviolet lamps to study photochemical processes. Plasmas of CH4, N2, CH3CN, NH3, O2, and H2, among other species, have been generated and the molecular products easily identified by the rotational spectrum, and via mass spectrometry and optical spectroscopy. Finally, the rotational spectrum of the lowest energy conformer of CH3CH2NHCHO (N-ethylformamide), a molecule previously characterized in microwave rotational spectroscopy, has been measured up to 116.5 GHz, allowing the accurate determination of its rotational and distortion constants and its search in space.

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An accurate determination of barrier heights at the HfO2∕Si interfaces

Journal of Applied Physics ◽

10.1063/1.1778213 ◽

2004 ◽

Vol 96 (5) ◽

pp. 2701-2707 ◽

Cited By ~ 87

Author(s):

Ragesh Puthenkovilakam ◽

Jane P. Chang

Keyword(s):

Accurate Determination ◽

Barrier Heights

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Headspace Solid Phase Microextraction Application for Pesticide Residues in Fruits and Vegetables

Arab Journal of Sciences & Research Publishing - المجلة العربية للعلوم و نشر الأبحاث ◽

10.26389/ajsrp.z14216 ◽

2016 ◽

Vol 2 (2) ◽

Author(s):

Abookleesh L Frage , Almrhag M. Omar , Zatout M. Massoud

Keyword(s):

Sample Preparation ◽

Solid Phase Microextraction ◽

Fruits And Vegetables ◽

High Efficiency ◽

Solid Phase ◽

Accurate Determination ◽

Chemical Properties ◽

Extraction Process ◽

Headspace Solid Phase Microextraction

Headspace solid phase microextraction, fundamental& principle with its application on the determination of various pesticides are reviewed in this article. Pesticides extraction as a sample preparation step prior to subsequent analysis is aimed to achieve a reliable and accurate determination of this contaminants residue in food. Fast and high efficiency extraction process with free solvent consumption and overall cost is achieved through headspace solid phase micro extraction. HSPME is an equilibrium process which depends on the physio-chemical properties of the analyte to be extracted. Sample preparation and extraction condition such as fiber coating, temperature, time etc, have a direct impact on the extraction efficiency and sensitivity of headspace technique.

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Physico-chemical characterization of bilirubin-10-sulfonate and comparison of its acid–base behavior with unconjugated bilirubin

Scientific Reports ◽

10.1038/s41598-021-92377-8 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Adam Čepa ◽

Veronika Dejmková ◽

Ladislav Lešetický ◽

Ivan Jelínek ◽

Stanislav Smrček ◽

...

Keyword(s):

Methodological Approach ◽

Accurate Determination ◽

Chemical Properties ◽

Cd Spectroscopy ◽

The Body ◽

Unconjugated Bilirubin ◽

Critical Threshold ◽

Bile Pigment ◽

Physico Chemical

AbstractUnconjugated bilirubin (UCB) is the end-product of heme catabolism in the intravascular compartment. Although beneficial for human health when mildly elevated in the body, when present at greater than a critical threshold concentration, UCB exerts toxic effects that are related to its physico-chemical properties, particularly affecting the central nervous system. The aim of the present study was to characterize bilirubin-10-sulfonate (ranarubin), a naturally occurring bile pigment, including determination of its mixed acidity constants (pKa*). Thanks to the presence of the sulfonic acid moiety, this compound is more polar compared to UCB, which might theoretically solve the problem with an accurate determination of the UCB pKa* values of its propionic acid carboxylic groups. Bilirubin-10-sulfonate was synthesized by modification of a previously described procedure; and its properties were studied by mass spectrometry (MS), nuclear magnetic resonance (NMR), infrared (IR), and circular dichroism (CD) spectroscopy. Determination of pKa* values of bilirubin-10-sulfonate and UCB was performed by capillary electrophoresis with low pigment concentrations in polar buffers. The identity of the synthesized bilirubin-10-sulfonate was confirmed by MS, and the pigment was further characterized by NMR, IR, and CD spectroscopy. The pKa values of carboxylic acid moieties of bilirubin-10-sulfonate were determined to be 5.02, whereas those of UCB were determined to be 9.01. The physico-chemical properties of bilirubin-10-sulfonate were partially characterized with low pKa* values compared to those of UCB, indicating that bilirubin-10-sulfonate cannot be used as a surrogate pigment for UCB chemical studies. In addition, using a different methodological approach, the pKa* values of UCB were found to be in a mildly alkaline region, confirming the conclusions of a recent critical re-evaluation of this specific issue.

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Rotational spectroscopy of isotopic species of methyl mercaptan at millimeter and submillimeter wavelengths: CH334SH

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935579 ◽

2019 ◽

Vol 627 ◽

pp. A41 ◽

Cited By ~ 2

Author(s):

Olena Zakharenko ◽

Frank Lewen ◽

Vadim V. Ilyushin ◽

Holger S. P. Müller ◽

Stephan Schlemmer ◽

...

Keyword(s):

Group Versus ◽

Rotational Spectroscopy ◽

Methyl Mercaptan ◽

Rotational Spectrum ◽

Experimental Accuracy ◽

Terrestrial Environment ◽

Natural Isotopic Abundance ◽

Molecular Core ◽

Submillimeter Wavelengths ◽

Millimeter And Submillimeter Wavelengths

Methyl mercaptan (CH3SH) is an important sulfur-bearing species in the interstellar medium, terrestrial environment, and potentially in planetary atmospheres. The aim of the present study is to provide accurate spectroscopic parameters for the most abundant minor isotopolog CH334SH to support radio astronomical observations at millimeter and submillimeter wavelengths. The rotational spectrum of CH334SH, which is complicated by the large-amplitude internal rotation of the CH3 group versus the 34SH frame, was investigated in the 49−510 GHz and 1.1−1.5 THz frequency ranges in natural isotopic abundance. The analysis of the spectrum was performed up to the second excited torsional state, and the obtained data were modeled with the RAM36 program. A fit within experimental accuracy was obtained with a RAM Hamiltonian model that uses 72 parameters. Predictions based on this fit are used to search for CH334SH with the Atacama Large Millimeter/submillimeter Array (ALMA) toward the hot molecular core Sgr B2(N2), but blends with emission lines of other species prevent its firm identification in this source.

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A quantitative approach to inner shell losses

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010010977x ◽

1978 ◽

Vol 36 (1) ◽

pp. 526-527 ◽

Cited By ~ 2

Author(s):

R.D. Leapman ◽

P. Rez ◽

D.F. Mayers

Keyword(s):

Energy Transfer ◽

Cross Section ◽

Cross Sections ◽

Accurate Determination ◽

Background Intensity ◽

Core Excitation ◽

Quantitative Basis ◽

Cross Section Differential ◽

Bound Electrons

Microanalysis by EELS has been developing rapidly and though the general form of the spectrum is now understood there is a need to put the technique on a more quantitative basis (1,2). Certain aspects important for microanalysis include: (i) accurate determination of the partial cross sections, σx(α,ΔE) for core excitation when scattering lies inside collection angle a and energy range ΔE above the edge, (ii) behavior of the background intensity due to excitation of less strongly bound electrons, necessary for extrapolation beneath the signal of interest, (iii) departures from the simple hydrogenic K-edge seen in L and M losses, effecting σx and complicating microanalysis. Such problems might be approached empirically but here we describe how computation can elucidate the spectrum shape.The inelastic cross section differential with respect to energy transfer E and momentum transfer q for electrons of energy E0 and velocity v can be written as

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Fast calibration of CBED patterns for quantitative analysis

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100149209 ◽

1993 ◽

Vol 51 ◽

pp. 674-675

Author(s):

M.A. Gribelyuk ◽

M. Rühle

Keyword(s):

Reciprocal Lattice ◽

Accurate Determination ◽

Incident Beam ◽

Crystal Thickness ◽

Structure Model ◽

Beam Direction ◽

Transmitted Beam ◽

Reciprocal Vector ◽

On Line

A new method is suggested for the accurate determination of the incident beam direction K, crystal thickness t and the coordinates of the basic reciprocal lattice vectors V1 and V2 (Fig. 1) of the ZOLZ plans in pixels of the digitized 2-D CBED pattern. For a given structure model and some estimated values Vest and Kest of some point O in the CBED pattern a set of line scans AkBk is chosen so that all the scans are located within CBED disks.The points on line scans AkBk are conjugate to those on A0B0 since they are shifted by the reciprocal vector gk with respect to each other. As many conjugate scans are considered as CBED disks fall into the energy filtered region of the experimental pattern. Electron intensities of the transmitted beam I0 and diffracted beams Igk for all points on conjugate scans are found as a function of crystal thickness t on the basis of the full dynamical calculation.

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Computer-Assisted High-Re Solution TEM

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100179567 ◽

1990 ◽

Vol 48 (1) ◽

pp. 162-163

Author(s):

F.A. Ponce ◽

H. Hikashi

Keyword(s):

Signal To Noise Ratio ◽

Accurate Determination ◽

Computer Software ◽

Video Camera ◽

Image Contrast ◽

Objective Lens ◽

Computer Assisted ◽

Optical Parameters ◽

Astigmatism Correction

The determination of the atomic positions from HRTEM micrographs is only possible if the optical parameters are known to a certain accuracy, and reliable through-focus series are available to match the experimental images with calculated images of possible atomic models. The main limitation in interpreting images at the atomic level is the knowledge of the optical parameters such as beam alignment, astigmatism correction and defocus value. Under ordinary conditions, the uncertainty in these values is sufficiently large to prevent the accurate determination of the atomic positions. Therefore, in order to achieve the resolution power of the microscope (under 0.2nm) it is necessary to take extraordinary measures. The use of on line computers has been proposed [e.g.: 2-5] and used with certain amount of success.We have built a system that can perform operations in the range of one frame stored and analyzed per second. A schematic diagram of the system is shown in figure 1. A JEOL 4000EX microscope equipped with an external computer interface is directly linked to a SUN-3 computer. All electrical parameters in the microscope can be changed via this interface by the use of a set of commands. The image is received from a video camera. A commercial image processor improves the signal-to-noise ratio by recursively averaging with a time constant, usually set at 0.25 sec. The computer software is based on a multi-window system and is entirely mouse-driven. All operations can be performed by clicking the mouse on the appropiate windows and buttons. This capability leads to extreme friendliness, ease of operation, and high operator speeds. Image analysis can be done in various ways. Here, we have measured the image contrast and used it to optimize certain parameters. The system is designed to have instant access to: (a) x- and y- alignment coils, (b) x- and y- astigmatism correction coils, and (c) objective lens current. The algorithm is shown in figure 2. Figure 3 shows an example taken from a thin CdTe crystal. The image contrast is displayed for changing objective lens current (defocus value). The display is calibrated in angstroms. Images are stored on the disk and are accessible by clicking the data points in the graph. Some of the frame-store images are displayed in Fig. 4.

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