Takashi Ishiwata

Infrared diode laser spectroscopy of the NO3 ν3 band

The N–O degenerate stretching band ν3 of the NO3 radical has been studied in the gas phase by infrared tunable diode laser spectroscopy. The NO3 radical was generated by the reaction of NO2 with an excess of O3. Zeeman modulation was employed to observe the paramagnetic absorption lines of 14NO3 and 15NO3 in the wavelength regions 1480–1500 and 1463–1479 cm−1, respectively. Only K’’=3n (n denoting an integer) transitions were observed, and the N’’=even members were missing from the K’’=0 manifold. These observations indicate that the NO3 radical belongs to D3h symmetry in the 2A2’ ground electronic state. The observed spectrum was analyzed using a symmetric‐top vibration‐rotation Hamiltonian including the spin‐rotation interaction. The main parameters thus obtained for 14NO3 are B3=0.455 22(11), C3=0.227 13(6), Cζ3=0.044 79(11), q3=0.001 624(33), t3= 0.000 000 458 0(43), B0=0.457 46(12), C0=B0/2 (fixed), ebb=0.0280(27), and ecc=0.1197(36) for v3=1, ebb=0.0277(28), and ecc=0.1117(34) for v=0, and ν0=1492.3...

A reinvestigation of the NO3 1492 cm−1 band

Ishiwata et al. [J. Chem. Phys. 82, 2196 (1985)] have recently observed an infrared diode laser spectrum of NO3 in the 1492 cm−1 region and have assigned it to the ν3 band in the X2A’2 state. However, some of the derived constants such as the Coriolis coupling and spin–rotation constants did not conform well with expected values. In the present study, the observation was extended so as to take combination differences, which led us to revise the previous assignment slightly and to remove all the anomalies in the lower (i.e., ground) state. A most important result of the present study is that a spin–orbit interaction constant aeff‖〈Lz〉‖ =0.17 cm−1 is indispensable to explain the spin splitting observed for the upper state. The first‐order Coriolis coupling constant of the upper state (ζ=0.19) remains essentially the same as in the previous study and differs considerably from the value calculated for the ν3 state (ζ=0.7). Possible explanations of these data are discussed in some detail to obtain more inform...

A Spectroscopic Study of the D(0u

The D( 0 u + ) ion-pair state of I2 has been analyzed by the optical–optical double resonance (OODR) technique. In a stepwise three-photon excitation scheme, D( 0 u + )–B3Π( 0 u + )–X1 Σ g + , the D( 0 u + ) state appeared in the OODR spectrum as the vibrational progressions consisting of O, Q and S branches in accord with the rotational selection rule of Δ J = 0 and ±2 for the coherent two-photon transition from the B3Π( 0 u + ) state. The D( 0 u + )–X1 Σ g + fluorescence was resolved to determine the absolute vibrational numbering of the D( 0 u + ) state. We derived Dunham parameters effective for ν = 0 through ν = 124 which were used to construct a Rydberg–Klein–Rees (RKR) potential curve.

Vibronic interactions in the NO3 radical

The 1492 cm−1 band of NO3 previously reported [J. Chem. Phys. 82, 2196 (1985); 93, 951 (1990)] exhibits some features in the upper state which are difficult to understand if the band is purely vibrational, i.e., the degenerate N–O stretching band in the ground electronic state. The two most conspicuous anomalies are a finite spin‐orbit coupling term which must be included in the Hamiltonian and a derived first‐order Coriolis coupling constant which is smaller than the calculated value. These anomalous features are explained by the vibronic interaction with excited 2E’ electronic states.

Fourier-transform infrared spectroscopy of the NO3 radical

Abstract The infrared spectrum of NO 3 was observed in the 1300–2800 cm −1 region by a high-resolution FT-IR spectrometer using the reaction of F atoms with HNO 3 . Three 2 E′- 2 A′ 2 bands were newly observed in the 1927, 2024, and 2155 cm −1 region in addition to the 1492, 2518, and 2585 cm −1 bands observed previously by a diode-laser system. The 2024 and 2155 cm −1 bands were analyzed by using a D 3h Hamiltonian to derive molecular constants. It was found that the obtained spin—orbit and Coriolis coupling constants in the 2 E′ states are very different for different vibronic states. The vibronic assignments of these bands are discussed.

Spectroscopic study on the iodine molecule by a sequential three‐photon excitation

A three‐photon absorption technique which utilizes a visible B 3Π0+u−X 1Σ+g transition followed by a simultaneous two‐photon absorption was applied to study an ion‐pair state of molecular iodine. The derived molecular parameters were Te=51 707 cm−1, ωe=131 cm−1, and Be=0.021 90 cm−1 for the F′(0+u) ion‐pair state, which dissociates to I−(1S)+I+(1D). The excitation of I2 to a single rovibronic level of the F′ state was achieved and its fluorescence spectrum showed two discrete band systems corresponding to the transitions to: (1) the ground state at higher vibrational levels; and (2) the weakly bound state (Te=19 286 cm−1, ωe=64 cm−1, and re=3.65 A) converging to the I(2P3/2)+I(2P1/2) products.

Identification of new ion‐pair states of molecular chlorine

Three new ion‐pair states of molecular chlorine have been identified by the double resonance method utilizing a sequential three‐photon absorption. Two independently tunable dye lasers were used to excite the chlorine molecules into a specific rovibronic level of the B 3Π0+u state, and subsequently into levels of ungerade excited states by a simultaneous two‐photon transition. The method enabled us to observe transitions to the low vibrational levels of ion‐pair states in the energy range of 7.3–7.7 eV, which were directly inaccessible from the ground state due to the small Franck–Condon factors. Their spectroscopic parameters were derived from the vibrational and rotational analyses of two separate isotope species, 35Cl–35Cl and 35Cl–37Cl. The two‐photon transitions from the B3Π0+u state to ion‐pair ones consisted of simple O, Q, and S branches. The polarization effect on their transition probability established that the symmetry of three ion‐pair states was 0+u in the Hund’s case c notation. The propert...

The ultraviolet photodissociation of Cl2O at 235 nm and of HOCl at 235 and 266 nm

The primary photochemistry of gas phase dichlorine monoxide (Cl2O) and of hypochlorous acid (HOCl) following excitation at 235 nm has been investigated using photofragment ion imaging to obtain the recoil velocity and angular distributions of the ground (2P3/2) and spin-orbit excited (2P1/2) atomic chlorine products. In the case of Cl2O, both Cl spin-orbit products exhibit angular distributions characterized by an anisotropy parameter, β=1.2±0.2, consistent with previous interpretations of the ultraviolet (UV) absorption spectrum of Cl2O which associate the broad intense absorption feature peaking at λ∼255 nm with excitation to a (bent) dissociative state of 1B2(C2v) symmetry. The recoil velocity distributions of the two Cl spin-orbit products are markedly different. The ground state atoms (which constitute >90% of the total Cl atom yield) are partnered by ClO fragments carrying significantly higher average levels of internal excitation. The slowest Cl atoms are most readily understood in terms of three b...

A spectroscopic study of the E(0+g ) state of Cl2 by optical–optical double resonance

An optical–optical double resonance (OODR) technique has been applied to study the E(0+g ) ion‐pair state of Cl2 correlating with Cl−(1S)+Cl+(3P2). Observations were made on the v’=0 through v’=23 levels of the 35Cl2 isotope species. A set of Dunham molecular constants was derived by a global weighted least squares fit of 474 transitions (all in cm−1 and 3σ in parentheses): Y00=57 819.366(38), Y10=251.954(15), Y20=−1.0318(19), Y30=2.235(64)×10−3, Y01=0.116 556(62), Y11=−6.403(56)×10−4, and Y02=−4.8(37)×10−8. The emission spectra of the E(0+g )–B 3Π(0+u ) system observed in the OODR experiments were interpreted on the basis of Franck–Condon factor calculations, which established the absolute v’ numbering of the E(0+g ) ion‐pair state.

Dynamics of the spontaneous formation of a planar phospholipid bilayer: A new approach by simultaneous electrical and optical measurements

An artificial lipid bilayer in planar form, well known as bilayer lipid membrane (BLM), spontaneously forms from a lipid droplet (L-α-phosphatidylcholine in n-decane and chloroform in this work) in an aperture of a thin partition in aqueous solution. The thinning dynamics of the lipid droplet or membrane has been studied by simultaneous capacitance and image recording, because the lipid membrane sandwiched by aqueous solutions can be considered as a parallel-plate capacitor. The simultaneous measurements have revealed the two-step thinning of the lipid membrane from its specific capacitance value: first, the initial droplet thins to yield a membrane of about 100 nm thickness (0.02 μF/cm2), and second, within this thin lipid membrane, a lipid bilayer of 4 nm thickness (0.42 μF/cm2) suddenly emerges and grows, keeping a bilayer structure. In addition, the simultaneous measurements have a time stamp, and thus can determine the trigger moment of the bilayer formation. The revealed dynamics provides the first ...