Yukari Matsuo

Rotational‐ and vibrational‐state dependence of transverse relaxation rate constants of OCS

The sensitivity of a microwave coherent transient spectrometer has been improved by two orders of magnitude. Rotational transitions in the ground and the vibrational excited states of ν2, ν1, and 2ν2 of OCS are systematically investigated to obtain the transverse relaxation rate constants. The calculation using the Anderson–Tsao–Curnutte theory gives a satisfactory explanation of the observed rotational‐ and vibrational‐state dependence of the rate constants.

Collisional relaxation among rotation–inversion levels in the highly excited vibrational state of NH3

Pressure broadening parameters of the visible overtone transitions to the v=5 state in the N–H stretching mode of 14NH3 are measured. It is found that the parameters show good similarity to those of the microwave region both in the rotational quantum number dependence and in the absolute values. Even in the high vibrational state, the collision induced transitions between inversion levels give dominant contributions to the broadening parameters. Well‐defined rotational quantum number dependence obtained in the present analysis also gives confirmation of the previous assignments of rotational structure in the overtone transitions.

Measurement and calculation of rotational relaxation rate constants in the ground and excited vibrational states of HCOOH

The transverse relaxation rate constants of the rotational transitions of HCOOH, 101←000, 202←101, 211←110, 312←313, 413←414, and 514←515 in the ground state and 101←000 in the ν9 vibrationally excited state are measured by a microwave coherent transient spectrometer. Highly sensitive detections of weak transitions are achieved by new methods of stabilizing the center frequency of modulated microwave and of removing the background noise. No remarkable difference between the rate constants of the ground and excited vibrational states is found. The collisional relaxation among considerably dense energy levels are theoretically investigated on the basis of the impact theory, where only the dipole–dipole interaction is considered. Contributions from a large number of rotational levels are taken into calculations of the cross sections. A good agreement between the experimental and the theoretical results is obtained.

Rotational relaxation of OCS by spherical and nearly spherical perturbers

Collision cross sections for the transverse relaxation of OCS by spherical and nearly spherical perturbers have been measured. The observed cross sections vary linearly with β=[I22/(I1+I2)2α22M]1/5, where I1 and I2 are the ionization energies of OCS and the perturber. α2 is the polarizability of the perturber, and M is the reduced mass of the colliding molecules. Calculations based on the Anderson–Tsao–Curnutte theory using a simple dispersion force model for the OCS–perturber interaction are in qualitative agreement with the experimental results. By doubling the strength of the dispersion forces used to model the OCS–perturber interactions, the calculated cross sections are brought into agreement with the measured ones. The observed linear relation between the cross section and β can be used to predict cross sections for other (polar molecule)–(nonpolar nearly spherical perturber) collisions.

Direct observation of inversion transitions in the v=5 state of NH3 by millimeter wave‐optical double resonance

A powerful method for detailed studies of the static and dynamic properties of molecules in highly excited vibrational states is presented. NH3 molecule is excited to the v=5 state in the N–H stretching mode by a pulsed dye laser and a subsequent transient change in the millimeter wave absorption due to the inversion transition in the excited state is observed before the distribution returns to thermal equilibrium. The determined inversion transition frequencies are more accurate by more than two digits than those reported in the previous work.

Inversion transition frequencies in the v=5 state of NH3 measured by millimeter wave‐optical double resonance

Eight new frequencies of inversion transitions in the v=5 state of NH3 have been determined by millimeter wave‐optical double resonance method. The transitions are definitely assigned and the accuracy in frequency determination has been improved by more than two digits.

Spectroscopic properties of cold rubidium atoms in a magneto-optic trap

Abstract We investigate spectroscopic properties of cold 85 Rb atoms in a magneto-optic trap. Both the transmission and the reflection spectra of the trapped atoms are recorded. The dressed-atom picture and the density-matrix formalism are appropriately used to explain the absorption profile around the F=3-F′=2,3,4 and F=2-F′=1 transitions. Around the trapping laser frequency, phaseconjugation signals are observed (reflectivity is about 10 −4 ), which are attributed to the degenerate and nearly-degenerate four-wave mixing.

Bond Localization of Molecular Vibration

Publisher Summary This chapter describes bond localization of molecular vibration. Several vibrational quanta tend to localize in a bond and each bond oscillates independently in higher vibrational states. The vibrational characteristics in the high energy level are quite different from those in the ground state; the collisional dynamics in well-defined rotational levels in high energy level and ground state is very similar. In lower vibrational level, the wave function is a well-defined function of the normal coordinate, while in higher vibrational level, the probability density distributes in the direction of a linear combination of the normal coordinates Q 1 and Q 2. The localization becomes appreciable in the v=3 state. A process of localization of vibrational energy is traced as a function of vibrational quantum number.

Dynamic and Static Properties of Molecules in Highly Excited Vibrational States

Molecules in highly excited vibrational states have been studied with great interest in recent years. Their energy level structure and dynamic behavior are directly concerned with mechanisms of multiphoton dissociation, chemical reaction, relaxation in the lasing medium, and so on. A localization of vibration energy into a particular bond may take place before the processes proceed. For detailed investigation of high vibrational states it is required that rotational constants and rotational relaxation rate constants in the individual vibrational states are measured.