Okitsugu Kajimoto

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.

4-(N,N-Dimethylamino)benzonitrile solvated by a polar molecule: Structural demand for charge-transfer state formation

Abstract Van der Waals complexes consisting of 4-(N,N-dimethylamino)benzonitrile and a polar molecule such as H 2 O and CF 3 H were produced in a free jet. The laser-induced fluorescence spectra of their 0-0 bands showed blue-shifts in contrast to the van der Waals complexes with rare-gas atoms. Their emission spectra did not contain any charge-transfer component which is known to be easily observed in a polar solvent. These facts are interpreted in terms of the structure of the van der Waals complexes.

Laser‐initiated half‐reaction. Vibrational and rotational state distribution of NO produced from the reactant pair O(1D)⋅N2O

The vibrational and rotational state distribution was measured for NO produced from the reaction O(1D)+N2O→2NO via a reactant pair O(1D)⋅N2O, which, in turn, formed by the 193 nm photolysis of the N2O dimer. The dimer was generated by the supersonic expansion through a pulsed nozzle. The distribution was determined by using the laser‐induced fluorescence of NO on its A–X transition. The rotational distribution was of the Boltzmann type characterized by a low temperature, 60–100 K, at each vibrational level measured. The vibrational distribution was found to be composed of the two components, one very cold and the other relatively hot. The experiment using an isotopically labeled N2O revealed that the vibrational energy was not equally distributed over two kinds of NO; the NO originally present in N2O was vibrationally cool while that formed from O(1D) and the terminal nitrogen of N2O was vibrationally hot. These results indicate that the reaction occurring is the abstraction of the terminal nitrogen by O(...

Benzonitrile and its van der Waals complexes studied in a free jet. II. Dynamics in the excited state: The effect of changing the degrees of freedom of partner molecules

The dispersed fluorescence spectra of the van der Waals (vdW) complexes consisting of benzonitrile and various partner species were observed in a free jet following a single vibronic level (SVL) excitation. For the vdW complexes with atomic species (Kr and Ar), the fluorescence was found to come from the initially prepared state and/or from the monomer produced by vibrational predissociation. On the contrary, in the case of benzonitrile–molecule complexes (H2O, N2O, and CF3H), only the fluorescence from the relaxed vdW molecule was observed. These features are interpreted in terms of a simple general scheme of predissociation. Vibrational predissociation is considered to be a composite of the four processes: (1) radiative decay of the prepared state; (2) intracomplex vibrational energy transfer producing a relaxed vdW complex; (3) radiative decay of the relaxed vdW complex; and (4) dissociation of the relaxed vdW complex. The difference in fluorescent state between atomic and molecular vdW complexes are c...

The charge-transfer state of 4-dimethylamino-3,5-dimethylbenzonitrile studied in a free jet

Abstract The formation of the charge-transfer (CT) state of 4-dimethylamino-3,5-dimethylbenzonitrile (TMABN) is studied in a supersonic free jet. In agreement with the observation by Rotkiewicz and Rubaszewska in the gas phase, the CT emission appears upon excitation of TMABN isolated in a free jet. The structureless LIF spectrum observed even in the supercooled compound suggests a significant change in geometry in the upper electronic states. From the excitation wavelength dependence, the emission was found to be composed of two kinds of fluorescence: one from the CT state and the other from a twisted higher excited S 2 state.

Vacuum UV photolysis of NH3: rotational distribution of NH(c1Π) and the heat of formation of NH

Abstract The rotationally resolved emission spectra of NH(c 1 Π) was observed in the vacuum UV photolysis of ammonia by Ar, Kr and H resonance lines. Hot rotational distribution was reconfirmed for photolysis by either the Kr or the H line, while, in the case of Ar, NH(c 1 Π) was found to be cold. From the maximum rotational line observed in the 123.6 nm photolysis, the heat of formation of NH is determined to be 90.2–91.3 kcal/mol.

Studies on the reaction N + N3 → N2(B 3Πg) + N2(X 1Σ+g)

Abstract Strongly enhanced N2 first positive emission N2(B 3Πg → A 3Σ+u) has been observed on addition of N atoms into a flowing mixture of Cl and HN3. The dependence of the emission intensity on N atom concentration gave a rate constant for the reaction N + N3 → N2(B 3Πg) + N2(X 1Σ+g) of i(1.6 ± 1.1) × 10−11 cm3 molecule−1 s−1. That for the reaction Cl + HN3 → HCl + N3 is (8.9 ± 1.0) × 10−13 cm3 molecule−1 s−1 from the decay of the emission. Comparison of the emission intensity in ClHN3 with that in ClHN3N gave the rate constant of the reaction N3 + N3 → N2(B 3Πg) + 2N2(X 1Σ+g) as 1.4 × 10−12 cm3 molecule−1 s−1 on the assumption that N + N3 yields only N2(B 3Πg) + N2(X 1Σ+g).

A laser-initiated half-reaction: No formation from N2O dimer via the N2O·O(1D) reactant pair

Abstract The laser-initiated half-reaction (N 2 O) 2 + 193 nm → N 2 O·O( 1 D) + N 2 → 2NO + N 2 has been observed by using a molecular beam mass spectrometer. A beam of nitrous oxide dimer was generated by supersonic expansion through a nozzle-skimmer system. When 193 nm ArF laser radiation was focused onto the beam, NO + was detected. The intensity of NO + was proportional to the (N 2 O) 2 concentration. The observed laser power dependence of the NO + ion intensity suggests the following three-step mechanism starting from (N 2 O) 2 : the photodissociation of one moiety of (N 2 O) 1 , followed by the intramolecular reaction producing NO, and two-photon ionization of the product NO to form NO + .

Crossed beam study of reaction of van der Waals molecule O+(NO)2 →NO*2+NO: Angle‐resolved chemiluminescence detection

Bimolecular reaction of NO dimer with O atom was studied by use of a crossed beam apparatus. NO dimer was generated by the supersonic expansion of NO seeded in He. Oxygen atom beam, generated by the microwave discharge, was crossed with (NO)2 beam and the chemiluminescence from the product NO*2 was measured as a function of the scattering angle. The angular distribution is anisotropic and peaking at θlab=0, with respect to (NO)2 incidence. This fact suggests sideways or backward scattering of O atom in (NO)2+O reaction.

Crossed beam study of the reaction of van der Waals molecule O+(NO)2→NO*2+NO

The reaction O+(NO)2 was studied by use of a crossed‐beam apparatus. An (NO)2 beam generated by the supersonic expansion crossed at right angles with a collimated effusive beam containing oxygen atoms which were formed by microwave discharge. The product NO*2 was detected by the chemiluminescence. The angular distribution of the product was measured by an angle‐resolved emission detection technique. The distribution has forward and backward peaks with respect to the oxygen atom incidence and indicates the occurrence of an intermediate complex in the course of the reaction. The angular velocity distribution, as well as the onset of the chemiluminescence, indicates that the reaction exothermicity appears mostly as internal energy of NO*2 . The remaining energy flows into the product translation and rotation; the vibrational freedom of the third‐body molecule is not effective as an energy absorber. The emission intensity was found to decrease with increasing relative collision energy. A sharp drop of the int...