Akihiro Sugita

Effect of molecular bending on the photodissociation of OCS

At 230 nm, the photodissociation of OCS via a hot band and a triplet state was investigated by selective probing of high rotational levels of product CO (J=45–67) with photofragment imaging spectroscopy: OCS(v=0)+hν(UV)→CO(X 1Σ+,J⩾65)+S(3P), OCS(v=1)+hν(UV) →CO(X 1Σ+,J∼65)+S(1D). Additional two-photon IR excitation of the UV photoprepared OCS with intense 1.06 μm laser pulses bleaches the UV processes listed above and induces a new excitation channel of OCS: OCS(v=0)+hν(UV)→OCS*, OCS*+2hν(IR)→CO(X 1Σ+,J∼74)+S(1S). The bending mode of OCS in the excited states plays a central role in the excitation and dissociation dynamics. Additionally, the alignment effect of OCS by nonresonant infrared laser pulse, which appears on the angular distribution of the photofragment, is discussed.

Control of photofragment velocity anisotropy by optical alignment of CH3I

A molecule placed in an electric field can be aligned because of the anisotropy of its polarizability tensor. As an alternative to high static electric fields, the electric field of a pulsed laser can be used for alignment. The alignment can be demonstrated by measurement of the control of the anisotropy of photodissociated fragments generated by polarized light. Sakai et al. have recently reported such an experiment on aligned iodine molecules [J. Chem. Phys. 110, 10235 (1999)]. This paper reports an independent finding of the same phenomenon with CH3I. General equations are presented for the degree of alignment and its control of the photodissociation amplitude. The control parameter for a symmetric top or linear molecule is −(α−αzz)(E2/2kT)P2(cos χ), where α is the mean polarizability, αzz is the element of the polarizability tensor along the symmetry axis, and χ is the angle between the E vectors of the aligning and dissociating lasers. The fragment velocity anisotropy can be increased or decreased by...

Effective interaction energy of water dimer at room temperature: An experimental and theoretical study

Buffer-gas pressure broadening for the nu(1)+nu(3) band of H(2)O at 1.34-1.44 mum for a variety of buffer gases was investigated at room temperature using continuous-wave cavity ring-down spectroscopy. The effective interaction energy of water dimer under room temperature conditions was evaluated from the pressure broadening coefficients for rare gases using Permenter-Seavers relation. Monte Carlo simulations were performed using ab initio molecular orbital calculations to evaluate the interaction energies for the water dimer at 300 K. In this theoretical calculation, the orientations of the two water molecules were statistically treated.

Controlling the branching ratio of the photodissociation of aligned Cl2 at 404 nm

Abstract Non-resonant infrared Nd 3+ :YAG laser pulses at 1.06 μm were used to align chlorine molecules in a cold molecular beam. The degree of alignment was demonstrated by measurement of the velocity anisotropy of the photofragment Cl ( 2 P 3/2 ) atoms from Cl 2 ( X 1 Σ g + )+404 nm → Cl 2 ( B 3 Π u + ,Ω=0)→ Cl ( 2 P 3/2 )+ Cl ( 2 P 1/2 ) . The branching ratio of the photoexcitation to Cl 2 ( B 3 Π u + ,Ω=0) with respect to Cl 2 ( 1 Π u ,Ω=1) was controlled, allowing the selectivity of the two different adiabatic photodissociation channels: Cl ( 2 P 3/2 )+ Cl ( 2 P 1/2 ) and Cl ( 2 P 3/2 )+ Cl ( 2 P 3/2 ).

Generation of broadband mid-infrared pulses by noncollinear difference frequency mixing

The generation of broadband mid-infrared (MIR) laser pulses by difference frequency mixing (DFM) is investigated. Two-color femtosecond pulses from a Ti:sapphire laser system are mixed in an AgGaS2 crystal using a noncollinear phase matching scheme. The relative bandwidth of the generated MIR pulse has been measured to be 23% of the central frequency, the broadest in DFM-based MIR sources reported thus far. It is found that a type-I crystal can yield a broader phase matching range of the spectrum than a type-II crystal within this scheme.