Quasicontinuum States Research Articles

Infrared Multiphoton Dissociation of C2F3Cl

The mechanism of infrared multiphoton dissociation of C2F3Cl was investigated by observing CO2 laser power dependences of a number of absorbed photon/molecule and reaction rate. A phenomenological model calculation shows that the absorbed energy is localized in two vibrational modes in quasicontinuum state.

Infrared–microwave double resonance spectroscopy of DCCCHO using the 3.51 μm He–Xe laser

Microwave spectrum of propynal-d1, DCCCHO, was investigated in the v2=1 excited state by an infrared–microwave double resonance method. The 3.51 μm He–Xe laser was magnetically tuned over ±0.1 cm−1 and used as an infrared radiation source. Eighteen pure rotational transitions in the excited state were observed and assigned. The observed spectrum was found to be badly perturbed by other vibrational states. In addition to the transitions within the v2=1 state, ten microwave transitions from the v2=1 to other vibrational states were observed. These intervibrational microwave transitions were discussed in relation to vibrational quasicontinuum states of polyatomic molecules.

Compatibility restrictions in the theory of antiresonance line shapes

The quasicontinuum correlation parameters that occur in the theory of antiresonance line shapes and radiationless decay, by virtue of being defined in terms of averages over the same set of quasicontinuum states, are shown to be restricted by conditions of mutual compatibility. These restrictions are analyzed in geometrical terms and some of their consequences are examined. A new correlation parameter λ is introduced and shown to qualitatively measure in many ways the overall consequences of correlations among the quasicontinuum couplings for many sparsely spaced states. A method is given for parametrizing the line shape and radiationless decay theory so as to satisfy the compatibility restrictions implicitly, thereby facilitating the analysis of experimental data. The application of the compatibility relations to the analysis of some recently reported line shape studies for molecules and solids is then discussed, including recent work on the optical absorption spectrum of boron-doped silicon.

Erratum: Coupling-strength incoherence and the theory of resonances for a system of several sparse states and quasicontinua

The phenomena of unimolecular radiationless decay and vibronic dissipative broadening in large molecules are studied by developing a theoretical treatment of a system of several sparsely spaced zero‐order states coupled to a dense set of states that have unlike physical character, thereby extending earlier work on the line shape for a single and a double resonance. Observable quantities, such as the absorption line shape, that involve averages over the dense states are shown to depend on diverse microscopic details of the quasicontinuum states only collectively through the values of a small number of matrix element correlation parameters and matrix element averages. The effects of interstate interactions on the values of the matrix‐element correlation parameters and matrix‐element averages are examined, and related sum rules are obtained. The physical consequences implied by uncorrelated matrix elements for nearby dense states are studied, and it is shown that relaxing the overly restrictive assumptions o...

Evidence for a molecular REC-effect in heavy ion collisions

Anisotropy spectra of the MOK X-ray transitions have been measured in F-Al, Al-Al and Cl-Al collisions as a function of the projectile energy. The measurements at higher energies indicate a new molecular effect due to transitions from quasicontinuum states to the MO 1sσ-orbitals.

Coupling-strength incoherence and the theory of resonances for a system of several sparse states and quasicontinua

The phenomena of unimolecular radiationless decay and vibronic dissipative broadening in large molecules are studied by developing a theoretical treatment of a system of several sparsely spaced zero-order states coupled to a dense set of states that have unlike physical character, thereby extending earlier work on the line shape for a single and a double resonance. Observable quantities, such as the absorption line shape, that involve averages over the dense states are shown to depend on diverse microscopic details of the quasicontinuum states only collectively through the values of a small number of matrix element correlation parameters and matrix element averages. The effects of interstate interactions on the values of the matrix-element correlation parameters and matrix-element averages are examined, and related sum rules are obtained. The physical consequences implied by uncorrelated matrix elements for nearby dense states are studied, and it is shown that relaxing the overly restrictive assumptions of earlier model treatments qualitatively changes the theoretical predictions obtained, generally in the direction of improved agreement with experiment.

Resonance line shapes in the Rydberg spectra of large molecules

The theory of line shapes in absorption to nearly degenerate states of large molecules is re-examined by relaxing the assumptions of the Bixon–Jortner model. The use of a single interaction strength to describe the coupling of a given sparse state to all members of the quasicontinuum of dissipative states is shown to produce an absorption intensity that vanishes at an energy determined independently of the assumed zero-order quasicontinuum level spacings. A more general theory is developed. The variation in coupling strength to nearby quasicontinuum states is shown to yield an absorption intensity that fails to vanish near resonance, and sometimes to suppress the characteristic features of the antiresonance line shape expected on the basis of simpler models, thus accounting for the scarcity of observable antiresonances and for some features of the naphthalene absorption spectrum. A new interference effect, involving the coalescence of neighboring absorption peaks into a single narrowed peak, is demonstrated.

Effects of High Pressure on the Far-Infrared Spectra of Paraelectric KH2PO4 and RbH2PO4

Using an opposed-anvil-type diamond cell, the infrared spectra of KH2PO4, RbH2PO4, and monoclinic RbD2PO4 have been measured in the 100–1400-cm−1 region up to pressures of 60 kbar and at several temperatures. The room-temperature spectrum of RbH2PO4 demonstrates the existence of a new high-pressure phase where the PO4 tetrahedra are distorted and the protons are ordered. This phase does not occur in monoclinic RbD2PO4. The results with KH2PO4 are not as dramatic as RbH2PO4. The effects of high pressure in the 300–600-cm−1 region are similar to those obtained on cooling below the Curie temperature (Tc), and have been interpreted in terms of resonance interference between a multiphonon quasicontinuum and discrete states of the distorted PO4 groups.