Curtis Marcott

Infrared circular dichroism associated with the C-H strecthing vibration of tartaric acid☆

The infrared circular dichroism associated with the C-H stretching vibration of tartaric acid-d4 [-CH(OD)COOD]2, has been measured. The observed CD spectra are most readily attributable to the chirality of the separate -CH(OD)COOD groups, rather than to a coupling between the groups.

Intensities of binary overtones and combinations in the infrared spectrum of CF4

The intensities of the binary overtone and combination bands in the infrared spectrum of CF4 have been measured. The dipole strengths of the allowed two‐quantum transitions have been determined from the measured intensities and have been compared with the dipole strengths calculated from the anharmonic terms in the intramolecular potential‐energy function. The discrepancies between the observed and calculated dipole strengths have been used to estimate the second derivatives of the molecular dipole moment with respect to the dimensionless normal coordinates.

Vibrational anharmonicity in CF4

A simple anharmonic force field, consisting of a general quadratic force field in curvilinear coordinates, augmented with principal cubic and quartic valence‐bond stretching force constants based on a Morse function, has been determined by least‐squares adjustment to the vibrational energies of CF4. Since this model did not give a value of the cubic normal‐coordinate force constant k344 in agreement with experiment, we considered a second force field identical to the first one except for the introduction of cubic stretch–bend–bend interaction force constants. These force fields have been used to calculate the tetrahedral anharmonic splittings of overtone and combination levels of CF4 and the calculated splittings have been compared with observed values determined by re‐examining the previously published infrared spectra of CF4 in liquid–argon solution.

Some theoretical considerations for magnetic vibrational circular dichroism spectra

Expressions are derived for the A terms, B terms, and associated partial anisotropy factors relevant for the magnetic vibrational circular dichroism (MVCD) spectra of molecules with nondegenerated ground states. These expressions are derived subject to the approximations of the harmonic fixed partial charge model and the condition of magnetic coupling among only the ground electronic state vibrational levels. Numerical values for partial anisotropy factors calculated from these expressions, when taken in conjunction with the recent MVCD data of Keiderling, suggest the importance of magnetic coupling of the ground electronic state with higher electronic states in the case of B terms. Symmetry constraints on the nonvanishing of such coupling terms also suggest the possible utility of MVCD data for providing spectroscopic and molecular structural information.

Three-quantum transition probabilities in the ν3 manifold of SF6 and the assignment of the observed 3ν3 transition in the i.r. spectrum

Abstract A theoretical expression has been derived for the intensity of a three-vibrational-quantum electric-dipole transition and has been used to calculate the intensities of the transitions from the ground state to the two F 1 u components of 3ν 3 of SF 6 . The calculated intensity of 1.02 × 10 −2 km/mol is in reasonable agreement with the observed intensity of 4.8 × 10 −2 km/mol.

3‐quantum transition probabilities in the ν3 manifold of UF6 and the assignment of 3ν3 in the observed infrared spectrum

Although there are two F1u components in 3ν3 of UF6 and transitions are allowed from the vibrational ground state to both, only a single band has been observed in the ir spectrum. These two states may be identified in a Cartesian representation of the normal coordinates as 3ν3x and 2ν3x+ν3y; on the basis of calculated intensities, the observed transition has been assigned to 3ν3x. The calculation of the dipole strengths required us to derive the octahedral splitting parameters G33 and T33 and these have been used to calculate the anharmonic splittings in the ν3 vibrational manifolds of 238UF6 and 235UF6.

A computer algorithm for the convenient normal-coordinate analysis of molecules with redundant coordinates

Abstract The traditional way of handling the vibrational problem in molecules with redundant internal coordinates becomes algebraically cumbersome when applied to larger molecules. The problem is much simpler when transformed into Cartesian coordinates since there are no redundancies in this space. This transformation is, however, nonlinear and therefore the linear internal-coordinate force constants contribute to the quadratic Cartesian ones and must be included. If the linear internal-coordinate force constants are known in advance, the solution of the normal-coordinate problem in Cartesian space is straightforward. This, unfortunately, is seldom the case. A new algorithm is proposed which allows the linear internal-coordinate force constants to be determined from a knowledge that the equilibrium configuration corresponds to a total minimum in the potential energy and a number of additional constraints equal to the number of redundant internal coordinates. This algebraically simple algorithm is shown to be fully equivalent to the more conventional ones.

A Vibrational Rotational Strength of Extraordinary Intensity. Azidomethemoglobin A

The asymmetric stretching vibration of the N3 - group in azidomethemoglobin A (azidometHb A) exhibits a vibrational circular dichroism (VCD) band (Fig. 1) of extraordinary and unprecedented intensity. Its rotational strength is three orders of magnitude greater than any heretofore noted. Integration of the VCD band gives a vibrational rotational strength (per tetramer) of 3 × 10 -40 (esu cm)2, a value typical for the electronic rotational strengths associated with the n → π* transition in saturated ketones.