K. Ohmori

Collision induced absorption in mercury–rare-gas collisions

The far-wing excitation and probe technique is applied to observe quasimolecular absorption bands on the blue side of the Hg 6 1S0–6 3P2 atomic line for the Hg–Ar, Hg–Kr, and Hg–Xe mixtures. It is found that the excitation of this band is followed predominantly by a rapid elastic half-collision scattering on the excited state potential yielding the nascent product state Hg(3P2). This gives direct evidence of the assignment of the absorption to the c 31→X 10 collision induced dipole transition of the Hg–rare-gas quasimolecules. A chance of nonadiabatic transition from the c state is negligibly small compared to the elastic scattering. Analytical procedures are presented to deduce the c–X transition dipole moment from the relevant potential energy curves by making use of the Hund’s coupling schemes of the molecular electronic states. The c–X transition dipole moment is estimated as a function of the internuclear distance and is incorporated into the analysis of the observed band profiles. The potential ener...

Far‐wing excitation study on the transit region of Hg 3P1→3P0 intramultiplet process in collisions with N2 and CO

Laser‐pump and probe approach has been applied to the far wings of Hg 3P1−1S0 resonance line broadened by collisions with N2 and CO to measure excitation spectra for the formation of Hg(6 3P0) and Hg(6 3P1). The excitation spectra are highly asymmetric with the red wing being much more extended than the blue wing. The absolute ratio of nascent yields of Hg 3P0 to 3P1 is determined as a function of the excitation wave number. From these measurements, it is found, commonly for Hg–N2 and Hg–CO systems, that (a) the nascent product ratio, Hg(3P0)/Hg(3P1), grows on the red‐wing surface (the A state) with increasing shift, Δν, of the excitation wave number from the line center and finally surpasses unity; (b) the blue‐wing surface (the B state) gives mostly Hg(3P1) but has a small chance to give Hg(3P0). Time constant τ0 for the A→3P0 process of Hg–N2 is found to change from 17 to 35 ns as the absorption distance Rc between Hg and N2 changes from 3.6 to 4.7 A. From these values of τ0, the transition probabil...

Spectroscopy of quasimolecular optical transitions: Ca(4s2?1S0leftrightarrow4s4p?1P,4s3d?1D2)-He. The influence of radiation width

We perform calculations using the semiclassical Fourier approach for quasimolecular spectra induced by thermal collisions of the excited calcium atom (Ca*) with the helium atom in the ground state (He) for the following quasimolecular optical transitions: (Ω = 0+,4s4p 1P)↔(Ω = 0+,4s2 1S0) and (Ω = 0+,4s3d 1D)↔(Ω = 0+,4s2 1S0) in the Ca-He quasimolecule. As a comparison with the experimental results obtained under gas-cell conditions, we average the spectra under study over the impact parameters and the Maxwellian distribution of the colliding particles. For the asymptotically forbidden Ca(4s2 1S0→4s3d 1D2)-He quasimolecular transition, the first comparison between the calculated spectral line profile and the experimental one is made not only in shape, but also in absolute value. We clarify the physical mechanisms for the initiation of a spectral line satellite at the position of the forbidden atomic transition being investigated. The reasonable agreement confirms that the spectral lineshapes of the asymptotically forbidden transitions are formed due to the interplay between the structure of the potential energy curves involved and the strong dependence of the radiative width.

Far‐wing excitation study of the reactions in the Hg–H2 collisional quasimolecules. II. Rovibrational distributions of HgH, HgD (X 2Σ+) formed from Hg–H2, D2, HD

We have applied the laser‐pump/probe and double‐beam absorption/dispersion approaches to the far wings of the Hg 3P1–1S0 resonance line broadened by collisions with H2, D2, and HD. Absolute reduced absorption coefficients of the Hg–D2 quasimolecules have been determined as a function of the wave‐number shift Δ from the resonance‐line center both in the red and blue wings. The nascent rotational distributions have been determined for the v=0 and 1 levels of HgH (X 2Σ+) and the v=0 level of HgD (X 2Σ+) formed from the Hg*(3P1)–H2, D2, and HD collisional–quasimolecular states A and B attained by the red‐ and blue‐wing excitation, respectively. Both of the intermediate states A and B give quite similar rotational distributions peaking around N≂18 for HgH and N≂25 for HgD insensitive to the excitation‐wave‐number shift Δ. However, a small difference is found: the red‐wing excitation gives larger populations in the low‐N levels than the blue‐wing one. The departing atom isotope effect is observed in these low...

Attosecond coherent control of the wave packet dynamics in the Hg–X van der Waals interaction

We have performed the double-pulse coherent control of nuclear wave packets, where the sequence of two identical femtosecond laser pulses generates two identical nuclear wave packets in the A30+ state of the single Hg–Ar van der Waals complex. The time delay between the two laser pulses is tuned with an accuracy in attosecond time scale to induce constructive and destructive interferences of the two nuclear wave packets. The interferogram measured by scanning the time delay shows a high-frequency oscillation with a period of 830 attoseconds. Wave packets have been manipulated in attosecond time scale for the first time.