Magnetic Vibrational Circular Dichroism Research Articles

Theory of Molecular Vibrational Zeeman Effects as Measured with Circular Dichroism.

We present a general theory that enables the first nonempirical computation of molecular vibrational Zeeman effects as are detectable with magnetic vibrational circular dichroism spectroscopy (MVCD). In this method, the second derivatives of the molecular magnetic moment appear to be essential to determine the observable MVCD intensities. Using a quasiharmonic approximation, computations based on our method allowed a band-to-band comparison of simulated to measured spectra. Given this new possibility of its reliable interpretation, MVCD spectroscopy may develop as a useful tool to yield detailed information on molecular vibrational states and structure, including achiral systems.

A Spectroscopic Study of Colchicine in the Solid State and in Solution by Multinuclear Magnetic Resonance and Vibrational Circular Dichroism

AbstractAlthough almost 200‐years‐old, several unknown aspects remain to be explored of colchicine, the unique available drug for acute flares of gout. In this article, we report density‐functional theory (DFT) studies of geometry, energy, and NMR; 1H‐, 13C‐, and 15N‐NMR chemical shifts and some spin‐spin coupling constants, including the complete analysis of the saturated part (ring B); the assignment of both enantiomers by NMR using a chiral solvating agent; solid‐state NMR experiments of the different forms of natural and racemic colchicine, and IR and vibrational circular dichroism (VCD) studies of these same forms.

Rotationally resolved magnetic vibrational circular dichroism of the paramagnetic molecule NO

Magnetic vibrational circular dichroism (MVCD) enables the measurement of molecular magnetic moments with modest spectral resolution. Due to its paramagnetism, NO gives a much stronger spectral response, about 3 orders of magnitude more intense, than do typical diamagnetic molecules. The molecule thus provides a convenient test for the experiment and theory of paramagnetic rotors. We have measured and analyzed the MVCD, equivalent to the molecular Zeeman spectra, of NO in co-linear magnetic fields of 0.1, 0.2, 2, 4 and 8 Tesla. Similar MVCD intensities were observed for both the (2)Π(1/2) and (2)Π(3/2) components of NO, particularly for high J values, which demonstrates a considerable deviation from pure Hund's case (a) for NO. The g(J)-values for the (2)Π(1/2) components of NO, which can be determined from our experimental spectra by moment analysis, agree well with the predicted values from Radford's theory. For the (2)Π(3/2) components, we tested this theory by simulating the MVCD and absorption spectra, and comparing them with our experimental spectra by use of moment analysis to show that they match well in terms of magnetic properties. While 0.2 T experiments easily develop sufficient MVCD for analysis of NO spectra and these low field intensities have a linear field dependence, spectra in the strong fields accessible in our study showed non-linear response due to onset of saturation effects. We also observed a strong field dependence for the absorption intensities for some (2)Π(3/2) components that was not encompassed in the theoretical model. Finally, a full coupling scheme provided analytical MVCD and absorption intensities that were in good agreement with the experimental values.

Circular Dichroism Techniques: Biomolecular and Nanostructural Analyses‐ A Review

This paper reviews the best known techniques using circular dichroism spectroscopy such as conventional circular dichroism (i.e. electronic circular dichroism), magnetic circular dichroisms (magnetic vibrational circular dichroism, x-ray magnetic circular dichroism), fluorescence detected circular dichroism, near-infrared circular dichroism, vibrational circular dichroism, Fourier transform infrared circular dichroism, high pressure liquid chromatography circular dichroism, stopped-flow circular dichroism, and synchrotron radiation circular dichroism. Also, we have described here the most important applications of circular dichroism spectroscopy in structural biochemistry and nanoscience.

Circular dichroism effect for linear molecules induced by a resonant circularly polarized pumping optical field.

In this paper we propose and discuss the laser-induced circular dichroism (LICD) effect, which is expected to occur in linear molecules pumped by a strong circular resonant light beam. The effect is to be detected via the absorption of a weak circularly polarized probe beam on another transition. Analogous to the external magnetic field in magnetic circular dichroism the resonant circular polarized pumping optical field can induce the nonzero antisymmetric rotational polarizabilities of a linear molecule, and cause the LICD effect. LICD contains three distinct contributions from M-dependent splittings of the sublevels mid R:JM due to the ac Stark effect, from the differences of Boltzmann statistical distributions among the ground state sublevels mid R:JM due to the ac Stark splittings, and from the changes of occupation probability in rotational sublevels mid R:JM due to the pumping effect. The fundamental formulas for the above three terms of LICD have been deduced by the density matrix method. As an example, the LICD for CO molecules have been calculated. The results indicate that in comparison with the rotationally resolved magnetic vibrational circular dichroism experiment, LICD may be measurable and form a basis of a different kind of CD spectroscopy.

Rotationally resolved magnetic vibrational circular dichroism

The rotationally resolved magnetic vibrational circular dichroism (RR MVCD) spectra of the diamagnetic molecules DCl and NH3 are analysed on the basis of theoretical simulation. Basic theoretical equations are derived for the RR MVCD dispersed intensity pattern from the conventional rovibrational energy level expression. This provides a convenient method for interpretation of MVCD spectra in terms of fundamental spectroscopic parameters. Good agreement was obtained between the simulated and the experimental data measured for DCl and NH3. Minor deviations from the theory occur in the dipole strength distribution for DCl, but this is corrected by measuring the A 1/D 0 ratio, from which the molecular g value can be determined for resolved transitions. Although magnetic properties of DCl and NH3 are known, this study demonstrates the ability of MVCD to provide an alternate method of determining molecular g-values as compared to classical microwave studies of the Zeeman effect. The data further show that exper...

Observations of rotational magnetic moments in the ground and some excited vibrational Σ states of C2H2, C2HD, and C2D2 by magnetic vibrational circular dichroism

Magnetic vibrational circular dichroism (MVCD) spectra of acetylene and its deuterated isotopomers have been recorded for the following Σ symmetry combination and overtone bands of C2H2: ν4+ν5; C2HD: ν4+ν5, 2ν4, 2ν5; C2D2: ν4+ν5, the ν3 fundamental for C2HD and C2D2; and the ν4→2ν4+ν5 and ν5→ν4+2ν5 hot bands for C2H2. For a Σg→Σu transition, the MVCD A terms observed must arise primarily from the rotational Zeeman effect. These negative A1/D0 values for low J″ transitions confirm that the sign of the rotational g-value for acetylene is positive. The rotational magnetic moments in both the lower and upper vibrational states were determined by comparison of moment analyses of experimental and simulated MVCD spectra obtained with a model Hamiltonian for acetylene. The gJ values in all the excited bending combination and overtone vibrational levels observed are smaller than those in the ground and the first excited stretching vibrational levels. This observation has been confirmed by theoretical simulation of the MVCD spectra of the ν4+ν5 combination band of C2H2. From these MVCD results, for C2H2, gJ(ground)=+0.0535±0.0033 and Δg(ν4+ν5)=−0.0061±0.0004; for C2D2, gJ(ground)∼gJ(ν3) =+0.0363±0.0048, Δg(ν4+ν5)=−0.0052±0.0031; and for C2HD, gJ(ground)∼gJ(ν3)=+0.0409 ±0.0069. These are the first quantitative, MVCD determinations of nondegenerate excited state g values distinctly different from the ground state. The decrease in g value correlates with off-axis deformation of the linear C2H2 rotation.

Rotationally resolved magnetic vibrational circular dichroism Experimental spectra and theoretical simulation for diamagnetic molecules

Rotationally resolved magnetic vibrational circular dichroism Experimental spectra and theoretical simulation for diamagnetic molecules

Direct measurement of the rotational g-value in the ground vibrational state of acetylene by magnetic vibrational circular dichroism

The magnetic vibrational circular dichroism (MVCD) spectra of the v4 + v5 combination band of acetylene was measured. from the result for the P(J″ = 1 → J′ = 0) rotational transition, the gJ-value in the ground vibrational state for C2H2 was determined to be +0.049 (±0.005). The sign of the gJ-value measured by MVCD confirms that the correct sign is positive as found in a revised molecular beam magnetic resonance experiment and predicted on the basis of molecular Zeeman studies of other molecules and magnetic effects on heat flow in acetylene. MVCD offers an exceptionally simple method of determining the sign of molecular g-values for both the ground and excited states.

Measurement of the vibrational Zeeman effect for HCF3 using magnetic vibrational circular dichroism

Magnetic vibrational circular dichroism (MVCD) for different vibrational modes of HCF3 have been measured. The vibrational Zeeman effect for the E-symmetry v4 and v5 modes have been determined for the first time from the solution and gas phase MVCD and absorption spectra. An analysis of the vibrational Zeeman effect for the other E-symmetry mode, v6, has been derived from the v3+v6 combination band MVCD and absorption spectra based on the vibronic coupling model. Comparisons of these results to predictions of different theoretical models have been used to analyze the sources of the observed Zeeman effect.

Measurements of the Rotational and Vibrational Zeeman Effect of Methane by Magnetic Vibrational Circular Dichroism

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMeasurements of the Rotational and Vibrational Zeeman Effect of Methane by Magnetic Vibrational Circular DichroismBaoliang Wang and Timothy A. KeiderlingCite this: J. Phys. Chem. 1994, 98, 15, 3957–3963Publication Date (Print):April 1, 1994Publication History Published online1 May 2002Published inissue 1 April 1994https://doi.org/10.1021/j100066a009RIGHTS & PERMISSIONSArticle Views173Altmetric-Citations10LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (846 KB) Get e-Alerts

Zeeman effect in T1u symmetry vibrational states of C60 fullerene

Theoretical analysis of the vibrational magnetic moments for the four T1u fundamental vibrational states of the C60 fullerene molecule is reported. An attempt to determine these moments is made in terms of a theory which includes both mechanical and vibronic contributions. At this level the theory leads to magnetic moments which are consistent in sign and relative magnitude with those measured for ν3=1183 cm−1 and ν4=1430 cm−1 vibrations of C60 using magnetic vibrational circular dichroism. Predictions for the lower energy vibrations at ν1=528 cm−1 and ν2=577 cm−1 are also provided. The moments of these latter transitions appear to arise almost totally from the mechanical (ground state) terms in the theory while those of higher energy modes have both vibronic and mechanical contributions. For the ν4 vibration the absolute magnitude of the combined vibronic and nuclear contributions was found to be larger than found in MVCD experiment. This may be due to the severe approximations implicit in the SCFPPP-CI method used.

Vibrational Zeeman effect for the nu 4 mode of haloforms (HCX3) determined by magnetic vibrational circular dichroism.

The magnetic vibrational circular dichroism (MVCD) spectra of the E-symmetry, ${\ensuremath{\nu}}_{4}$ modes of ${\mathrm{HCCl}}_{3}$, ${\mathrm{HCBr}}_{3}$, ${\mathrm{HCI}}_{3}$, and ${\mathrm{DCCl}}_{3}$ are presented. In each case, an MVCD A term indicating a first order vibrational Zeeman effect is observed. The vibrational g values for the ${\ensuremath{\nu}}_{4}$ mode of these haloforms were determined for the first time by moment analysis of the MVCD and absorption spectra. A partially charged ``elastic bar'' model is proposed to qualitatively explain the observed MVCD A terms.

Rotationally Resolved Magnetic Vibrational Circular Dichroism of Hydrogen Chloride and Deuterium Chloride

The magnetic vibrational circular dichroism (MVCD) spectra of HCI and DCI are presented. The average rotational g-value of H35Cl in the first excited vibrational states was determined to be 0.45 l and 0.449 for the P and R branches, respectively, using moment analysis of the MVCD bandshapes. In addition, the gJ-values of H37Cl, D35Cl, and D37Cl were measured for the first time. Within our experimental error, the gJ-values obtained were consistent with the accepted gJ-values for the ground state of H35Cl and with theoretically calculated gJ-values for the other isotopomers. The results show that MVCD can provide an alternative method to microwave spectroscopy or molecular beam magnetic resonance spectroscopy for determining rotational g-values.

Rotational Zeeman effect in carbon monoxide as determined by magnetic vibrational circular dichroism

The magnetic vibrational circular dichroism (MVCD) of carbon monoxide has been measured by use of a Fourier transform infrared vibrational circular dichroism spectrometer with an 8 T magnet. At 0.5 cm−1 resolution, the spectra are rotationally resolved, and both the sign and the magnitude of the g-factor for the rotational Zeeman effect in C≡O can be determined using moment analysis to deconvolve the MVCD band shape. A rotational g value of −0.262 was obtained with an estimated error in accuracy of ±0.026 and a precision of ±0.011. Averaging individual gJ determinations for more than 30 transitions in the R- and P-branches showed a much higher precision in the measurement. That this value agrees with the results of earlier, more precise, microwave-based measurements as well as theoretical determinations of gJ confirms that MVCD can be used as an alternate method to determine molecular Zeeman g factors.

Theoretical analysis of magnetic vibrational circular dichroism for 1,3,5-trihalobenzene derivatives

The theoretical of magnetic vibrational circular dichroism (MVCD) A terms is reported for the degenerate ν 9 and ν 10 vibrations of sym-C 6H 3X 3 (X=D, Cl, Br) molecules. An attempt to determine the A 1/ D 0 ratios for A′ 1→E′(ν 9) and A′ 1→E′(ν 10) fundamentals is made in terms of a theory which includes both mechanical and vibronic contributions to MVCD and absorption spectra.

Magnetic vibrational circular dichroism of C 60

The magnetic vibrational circular dichroism spectra of C 60 fullerene in solution are presented for excitation of the 1430 and 1183 cm −l t t1u -symmetry fundamental vibrations. These transitions give rise to A-term MVCD of opposite sign ( A 1 / D 0 =−3.8 and l.1 × 10 −4 , respectively) which are similar in magnitude to that of benzene. Using the MCD spectra for the two lowest-energy 1 T 1u electronic excitations of C 60 , the single excited-state vibronic coupling model correctly predicts the sign of one of the MVCD bands but underestimates both magnitudes.

Vibronic theory of magnetic vibrational circular dichroism in systems with fourfold symmetry: Theoretical analysis for copper tetraphenylporphyrin

A vibronic theory which includes multimode and multistate effects is developed to study magnetic vibrational circular dichroism (MVCD) and absorption spectra for molecular systems with fourfold symmetry. The MVCD and absorption spectra of the e fundamental transition and its combinations with infrared inactive modes are discussed in some detail to demonstrate the importance of electric and magnetic anharmonicity arising from vibronic coupling. The theory is applied to experimental MVCD spectra for the CuTPP molecule.

Magnetic vibrational circular dichroism of ammonia

We have measured the magnetic-field-induced circular dichroism of the A 1 symmetry (υ 2 ) and the E symmetry (υ 4 ) deformation modes of the NH 3 and ND 3 . At 0.5 cm -1 resolution, the spectra are partially rotationally resolved; and we can determine the sign and calculate the magnitude for the g factor of the rotational Zeeman effects observed by use of moment analysis of the rotationally resolved bands

Rotationally resolved magnetic vibrational circular dichroism of methane

Magnetic-field-induced circular dichroism of the ν 4 mode of methane at 0.5 cm −1 resolution is reported. For the first five members of the R branch, A 1/ D 0 is approximately constant, averaging −4.8 × 10 −4, which corresponds to an average g J of + 0.44. This agrees in sign with and is ≈ 40% higher than the magnetic resonance results for the ground state of methane. The difference may be due to experimental error or to vibrational magnetic moment contributions. The consistency of g J implies that the MVCD depends primarily on the change in M J in each transition.