Lloyd Seamans

Theorem Useful for Interpretation of Magnetic Circular Dichroism Spectra

It is shown that the magneto‐optical activity associated with a symmetry‐forbidden transition is of second or higher order in any perturbation and that the contributions to the magnetic rotational strengths of perturbations belonging to different irreducible representations are additive. This theorem can be useful in analyzing the vibrational structure of a forbidden spectral band and in elucidating the conformations of molecular systems. The problem of the origin dependence of the magnetic rotational strengths is also discussed.

Calculation of vibronic magnetic rotational strengths in formaldehyde

The magnetic rotational strengths (MRS) associated with the non‐totally‐symmetric vibrations in formaldehyde are calculated with CNDO/2 wave functions. The effects of configuration interaction are examined. We have also identified a single term that dominates the MRS. This raises the possibility of an economy of thought in attempts at correlating MRS data with molecular structure in the case of magnetic dipole allowed transitions.

Partial reduction of aquomethemoglobin on a sephadex G-25 column as detected by magnetic circular dichroism spectroscopy and revised extinction coefficients for aquomethemoglobin

In a typical preparation of aquomethemoglobin, oxyhemoglobin is oxidized with potassium ferricyanide, and the resultant mixture of methemoglobin and potassium ferro- and ferricyanides is separated on a Sephadex G-25 column. We find that about 1% of the heme is reduced on the column and is eluted with the methemoglobin. Magnetic circular dichroism spectra show that the reduced species is oxyhemoglobin. Magnetic circular dichroism is more sensitive than is absorption spectroscopy to small amounts of oxyhemoglobin in such solutions; we can detect its presence at the 0.1% level. A redetermination of the extinction coefficients for methemoglobin gives a value of 0.80 for the absorbance ratio A570A630 at pH 6. This value lies clearly outside the currently accepted range of 0.83 to 0.87.

Magnetic circular dichroism studies. XXXIII. The MCD spectrum of formaldehyde vapor

Abstract The MCD spectrum of formaldehyde in the vapor phase has been measured and analyzed. Triplet bands occur with unusually high ellipticity, allowing identification of several new singlet-triplet bands. Also, an additional singlet progression, based on two quanta of the out-of-plane band and a single quantum of the antisymmetric CH stretch, has been identified.

Magnetic circular dichroism studies—XXXI. Thioketones

Abstract The magnetic circular dichroism associated with the n -π* transition of several thioketones is reported and evidence is presented that the lowest energy band is of singlet-triplet origin.

Theoretical analysis of the magnetic circular dichroism spectrum of carbon disulfide

The upper level of the near‐ultraviolet absorption system of carbon disulfide (the R system) is the B2 spin‐multiplet component of a 3A2 state. A theoretical analysis of the magnetic circular dichroism spectrum of the R system shows that if, as has been assumed previously, the A1 and B1 spin‐multiplet components of the 3A2 state are degenerate, they lie above the B2 component. This result is at variance with earlier conclusions. The only ordering of the spin‐multiplet components which is consistent with all available data is one in which the A1 and B1 components are nondegenerate, with both of these components lying below the B2 component. The available data are insufficient to assign the relative ordering of the A1 and B1 components.

The magnetic circular dichroism spectrum of carbon disulfide

The magnetic circular dichroism spectrum of carbon disulfide vapor in the 300–380 nm region is reported and analyzed. The signs of the A terms associated with the P and R rotational branches of the triplet bands are negative and positive, respectively. These data are used in an accompanying theoretical paper (following paper in this journal) to calculate the zero field splittings in the 3A2 state of CS2.

The vapor phase magnetic circular dichroism spectrum of the 3Au ← 1Ag excitation of glyoxal

Abstract The vapor phase magnetic circular dichroism spectrum of the 520 nm band system of glyoxal is reported. The vibrational analysis of this spectrum, and its temperature dependence, extend and confirm the assignments made by Ramsay and his collaborators from magnetic rotation and emission data.

Magnetic circular dichroism of the 3B3μ ← 1 Ag excitation in pyrazine

Abstract The magnetic circular dichroism spectrum of the lowest lying singlet—triplet transition of pyrazine is reported. The experimental data are in accord with theoretical predictions based upon the assumption of Hunds case (b) coupling in the 3B3u state.

Theoretical analysis of the MCD spectra of some singlet-triplet transitions in formaldehyde

Abstract A recently developed theoretical treatment of the magneto-optical activity of singlet-triplet transitions in molecules which are near-symmetric rotors is employed in simulation of the MCD spectra associated with some singlet-triplet transitions in formaldehyde. The theoretical results are compared with the relevant experimental data, and the agreement between theory and experiment is found to be satisfactory.