Robert E. Linder

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.

Magnetic circular dichroism spectroscopy: A definitive method for the determination of urinary porphyrins☆

Abstract The application of MCD for the determination of urinary porphyrins is assayed by specific application to the screening of workers exposed to lead arsenate. The definitive nature of this new spectroscopic method arises from: (1) its sensitivity to as little as 0.02 μg/ml of porphyrin dication; (2) its freedom from interference caused by other substances; (3) the highly characteristic shape of the MCD bands exhibited by porphyrin dications; and (4) the high information content of the MCD spectrum.

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.

Vibronic magnetic rotational strengths in the B2u state of benzene

The vibronic magnetic circular dichroism (MCD) spectrum of the electronically forbidden 260 nm 1A1g→1B2u transition in benzene is analyzed in terms of e2g vibrational modes. The negative MCD progression is aasigned to the e2g 608 cm−1 and 1596 cm−1 modes and the positive progression to the e2g 1178 cm−1 and 3056 cm−1 modes. Experimental MCD and absorption spectra of benzene and benzene‐d6 in solution at room temperature and liquid nitrogen temperature are reported. Magnetic rotational strengths and oscillator strengths associated with each of the four e2g vibrations in benzene and benzene‐d6 have been calculated by two different methods: a perturbation treatment involving the π electrons only, and a CNDO calculation for a geometry in which the nuclei are distorted along a normal coordinate. The results of the two calculations agree reasonably well with each other and with experiment. Two terms that dominate the magnetic rotational strengths are identified.

Magnetic circular dichroism studies XXXIV: Improved instrumentation for MCD measurements

Abstract The use of a 15-kG electromagnet in conjunction with a circular dichrometer of enhanced sensitivity affords MCD spectra of quality comparable to those obtained using a superconducting magnet and an instrument of lower sensitivity. To demonstrate this, the MCD spectra of zinc octaethylporphyrin, human serum albumin, a microsomal suspension containing cytochromes P -450 and b 5 , adenine, and benzene in the vapor phase are reported. The convenience, economy of operation, and availability of electromagnets should be a major incentive for the utilization of this spectroscopic technique in a variety of potentially interesting areas in chemistry and biochemistry.

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.