Soji Tsuchiya

Vibrationally highly excited acetylene as studied by dispersed fluorescence and stimulated emission pumping spectroscopy: Vibrational assignment of the feature states

Author Institution: Department of Chemistry and George R. Harrison Spectroscopy Laboratory, Massachusetts Institute of Technology; Department of Pure and Applied Sciences, The University of Tokyo

Vibrational level structure of highly excited SO2 in the electronic ground state. II. Vibrational assignment by dispersed fluorescence and stimulated emission pumping spectroscopy

The dispersed fluorescence (DF) spectra for the fluorescence emitted from eight single rovibronic levels in the C 1B2 state are observed. The vibrational quantum numbers for these levels are (v’1,v2,v’3) =(0,0,0), (0,1,0), (0,2,0), (0,0,2), (1,0,0), (1,1,0), (1,2,2), and (3,1,0). The 484 vibrational levels distributed between 4300 and 21 600 cm−1 in the electronic ground state X 1A1 are identified based on the assignment of the 1388 transitions in the DF spectra. The vibrational level energy is expressed by an anharmonic expansion with 19 coefficients and the vibrational quanta for the three normal modes. The combination analysis of the DF and stimulated emission pumping spectra having the same upper rovibronic level clarifies the vibrational level structure in the vibrationally highly excited region above 17 000 cm−1.

Interatomic potentials of A 30+ and B 31 states of HgHe, HgNe, and HgAr van der Waals complexes

Rotational structures of A–X and B–X vibronic transitions of HgHe, HgNe, and HgAr van der Waals (vdW) complexes formed in supersonic free jets have been investigated. An analysis of the rotational contours shows that rotational structures for the six isotopic species, mHgHe, mHgNe, or mHgAr (m=204,202,201,200,199, and 198), are overlapped, and the observed isotopic splittings are utilized for the definite assignment of the vibrational quantum numbers in the A and B states. Based on the vibrational level spacings and the rotational constants, interatomic potentials for the A and B states of HgNe and HgAr are determined with good accuracy. In the case of the B state of the 199HgRg and 201HgRg (Rg=Ne or Ar), magnetic dipole hyperfine splittings are observed and analyzed.

Benzonitrile and its van der Waals complexes studied in a free jet. I. The LIF spectra and the structure

The van der Waals (vdW) complexes consisting of benzonitrile and various partner species were formed in a free jet and their laser‐induced fluorescence (LIF) spectra were recorded. For all the species chosen as partners (Ar, Kr, N2O, CF3H, and H2O), the LIF spectra showed a red shift relative to that of benzonitrile monomer. The spectral shift increased with increasing dipole moment of the partner species owing to the large dipole–dipole interaction between the partner species and benzonitrile whose dipole moment amounts to 4.14 D. With the aid of computer simulation, the rotational contours of the LIF spectra of the benzonitrile dimer and benzonitrile–Ar complex were analyzed. The dimer was found to be in planar form with the two CN groups facing each other in an antiparallel geometry, whereas in the Ar complex the Ar atom lies over the benzene ring slightly leaning toward the CN group.

State‐specific unimolecular reaction of NO2 just above the dissociation threshold

Photofragment excitation (PHOFEX) spectra of NO2 are observed by monitoring the specific quantum states of a fragment NO (2Π1/2;v=0, J=0.5–6.5) in the energy region 0–160 cm−1 above the dissociation limit to NO (2Π1/2) and O (3P2). Preparation of NO2 in a quasibound eigenstate above the dissociation limit is attained by the combination of extremely cooled (∼1 K) parent NO2 in a supersonic jet and a high resolution (∼0.05 cm−1) photolysis laser. The dissociation rate constants are obtained from the peak width of PHOFEX spectra and the smallest rate constant is k=8.5×109 s−1, in the energy region where only J=0.5 of NO (2Π1/2; v=0) is produced. The observation that the rate constant increases stepwise when a new product channel J=1.5 opens implies that the transition state is a loose complex. This behavior of the rate constant is direct experimental proof of the statistical theory of the unimolecular reaction process. The product state distribution of NO fluctuates depending on the quasibound state of NO2, ...

Laser-induced fluorescence spectroscopy of He-, Ne-, Ar-, and Kr-aniline van der Waals complexes in a supersonic free jet. Analysis of rotational contours

Abstract Laser-induced fluorescence spectra of the binary van der Waals (vdW) complexes of aniline with rare gas atoms (He, Ne, Ar, and Kr) in a supersonic free jet were observed. The rotational contours of their spectra were analyzed to determine the geometrical structures. The vdW bond lengths of the He-, Ne-, and Ar-aniline complexes in the X 1 A′ state are found to be 3.65(10), 3.35(4), and 3.50(4) A, respectively, while those in the A 1 A″ states for the Ne-, Ar- and Kr-aniline complexes are found to be shorter than those in the X 1 A′ state by 0.05(4), 0.08(3), and 0.15(10) A, respectively. The observed frequency shifts of the bands of the complexes relative to that of free aniline are in good correlation with the polarizabilities of the rare gas atoms.

Vibrational level structure of highly excited SO2 in the electronic ground state as studied by stimulated emission pumping spectroscopy

The stimulated emission pumping (SEP) spectroscopy is applied to SO2 cooled rotationally in a supersonic free jet to investigate the vibrational and rotational level structure in the 17 300–17 900, 21 400–21 500, and 22 200–22 500 cm−1 regions of the electronic ground state. It is concluded that respective vibrational levels are found to couple with each other by the network of Fermi and Coriolis interactions on the basis of the following grounds: (1) there are a number of Fermi pairs of the vibrational levels, and (2) the number of vibrational levels identified as the final states of the SEP transitions increases for rotational levels with larger rotational quantum numbers J and Ka. The distribution of the nearest neighbor vibrational level spacing shows that the vibrational quantum dynamics in the observed regions is almost quasiperiodic and the onset of the quantum chaos is estimated to be above 17 900 cm−1.

Interatomic potentials of HgXe van der Waals complex formed in supersonic jets as studied by laser induced fluorescence spectroscopy

The laser induced fluorescence spectra of HgXe formed in a supersonic free jet of a He/Xe/Hg mixture were observed to determine the interatomic potentials between Hg and Xe in the X 10+, A 30+, and B 31 states. The dissociation energies for the X, A, and B states are 254, 1457, and 172 cm−1, respectively, with the equilibrium interatomic distances of 4.25, 3.25, and 4.47 A for the respective states. It is found that the potential shape for the X and B states can be represented in good approximation by a Morse function, though this function may not reproduce the potential for the A state especially in the vicinity of high vibrational levels (v′>16).

Microwave kinetic spectroscopy of reaction intermediates: O+ethylene reaction at low pressure

A microwave spectroscopic method has been developed to study elementary reactions in real time through in situ observation of rotational spectra of reaction intermediates such as free radicals with lifetime as short as 1 ms. This method was applied to the O(3P)+ethylene reaction in order to assess the roles of (a) vinoxy+H and (b) CH3+CHO channels in the initial process. The reaction was initiated by irradiating an N2O/C2H4 mixture containing a trace amount of mercury with the 253.7 nm mercury resonance line, and the time evolution of vinoxy, HCO, and H2CO was followed by measuring their microwave absorption intensities as functions of time. The branching ratio was thus determined to be 0.4±0.1 and 0.5±0.1 for (a) and (b), respectively, at the sample pressure of 30 mTorr. The present result agrees with those obtained by Hunziker et al. [J. Photochem. 17, 377 (1981)] using much higher pressures of samples, but is not compatible with the observation of Buss et al. [J. Photochem. 17, 389 (1981)] that (a) is ...

Rovibronic level structure of electronically excited acetylene (A1Au) in a supersonic jet as studied by laser-induced fluorescence and Zeeman quantum beat spectroscopy

Abstract Laser-induced fluorescence (LIF) spectra of the A 1Au- X 1Σg+ transition of jet-cooled acetylene were measured resolution to resolve the respective rovibronic levels in the A nv′3 vibrational states. Most of rotational levels of the nv′ and 4) state split into several levels, while level splitting occurs scarcely for those in the 2v′3 state. The observed radiative lifetimes of the respective levels are different from each other. Especially, the average lifetime of levels in the 3v′3 state is relatively long compared with those in the other states. The fluorescence from a number of levels decays in an oscillatory manner under a weak magnetic field. This phenomenon is attributed to a coherent interaction between the Zeeman sublevels, from which a magnetic moment, i.e., a g-factor, can be determined characteristic to each level. A large g-factor assigned to a level implies that the level couples strongly with a triplet state. Long lifetimes and large g-factors found for levels in the 3v′3 state imply that these levels couple with triplet states more efficiently than other levels in the 4v′3 or 2v′3 state. Besides the Zeeman quantum beat, a quantum beat ascribed to level anticrossing between a level in the A nv′3 state and a nonfluorescent level is found for a number of excited levels. These anticrossings are due to interaction with its strength of the order of MHz, and ascribed to couplings with vibrationally highly excited levels in the X state.