Time-resolved infrared diode laser spectroscopy of the ν1 (C-O stretch) band of the CoCO radical

Infrared spectrum of the cobalt carbonyl radical CoCO produced by the 193 nm excimer laser photolysis of cobalt tricarbonyl nitrosyl Co(CO)₃NO was observed by time-resolved diode laser spectroscopy. More than 600 lines were identified as belonging to the ν₁ (C-O stretch) fundamental band, consisting of the Ω=5/2 and 3/2 subbands, and the associated hot bands , , , and . The ²Δ_i electronic ground state of CoCO was experimentally confirmed. The ν₁ band origins are 1974.172582(93) cm⁻¹ and 1973.53178(14) cm⁻¹ for the Ω=5/2 and 3/2 subbands, respectively. The rotational constant in the ground state was determined as B₀=4427.146(50) MHz. The centrifugal distortion constant D₀=1.1243(68) kHz was obtained for the Ω=5/2 substate of the ground state. The equilibrium rotational constant B_e=4435.44(14) MHz was derived, together with the vibration-rotation interaction constants.     

Parametric search: three new applications

Parametric search is a useful tool in geometric optimization. Invented by Nimrod Megiddo in 1983, it has been widely used in computational geometry. Unfortunately, this technique has rarely been used in the combinatorial optimization community in China. In this paper, we introduce parametric search via three new geometric optimization applications.     

Halogen-substituent effect on the spectroscopic properties of 2-phenyl-6-dimethylaminobenzothiazoles

6-Dimethylamino-2-phenylbenzothiazole (1-H) is a push-pull benzothiazole fluorophore mimicking the firefly oxyluciferin structure. We newly prepared 7-chloro and 7-bromo derivatives of 1-H and its 4-acetyl derivative (2-H), and their spectroscopic and photophysical properties were investigated. The halogenated derivatives showed the blue-shifted electronic absorption maxima and fluorescence emission maxima compared to 1-H and 2-H, resulted from the deformations of the NMe₂ groups and the electron withdrawing properties of the halogen groups. In addition, the halogen substitutions accelerate intersystem crossing by heavy atom effect, resulting in a decrease in fluorescence quantum yields. Interestingly, however, the halogenated derivatives of 2-H still showed moderate fluorescence quantum yields. The halogenation effect is one of the guides to design push-pull benzothiazole fluorophores for tuning fluorescence properties.     

Photoswitching of single association force between a pair of photoionizable spirobenzopyrans

We have measured the single intermolecular force of a typical photoionizable molecule, spirobenzopyran, by means of atomic force microscopy, which has proven to be useful in measuring directly single molecular forces. The spirobenzopyran moiety was immobilized covalently on both Au-coated probe tips and substrates by use of a self-assembled monolayer of a hexanethiol derivative incorporating a terminal spirobenzopyran moiety, 1'-(6'-mercaptohexyl)-3',3'-dimethylindolino-6-nitrospiro-(2H-1-benzopyran-2,2'-indoline). Force curve measurements were carried out using the spirobenzopyran-modified probe tip and substrate under dark conditions and in situ UV light irradiation. The adhesion force observed in a polar solvent (i.e., ethanol) was increased substantially under in situ UV light irradiation, which caused photoisomerization of the spirobenzopyran moiety bound to both tip and substrate from its electrically neutral spiropyran form to the corresponding zwitterionic merocyanine one. Statistical analyses of the observed force by autocorrelation technique have revealed that the photoionization enhanced by UV light caused a remarkable increase in the single intermolecular force of the photochromic compound.     

alpha-Aminoallylation of aldehydes in aqueous ammonia

alpha-Aminoallylation of aldehydes in aqueous ammonia has been developed; commercial aqueous ammonia was successfully used, and this method does not require anhydrous conditions thus leading to easy and practical operations.     

Measurement of the photonic de broglie wavelength of entangled photon pairs generated by spontaneous parametric down-conversion

Using a basic Mach-Zehnder interferometer, we demonstrate experimentally the measurement of the photonic de Broglie wavelength of entangled photon pairs (biphotons) generated by spontaneous parametric down-conversion. The observed interference manifests the concept of the photonic de Broglie wavelength. We also discuss the phase uncertainty obtained from the experiment.     

An ethoxy intermediate in ethanol dehydration on Brønsted acid sites in zeolite

Acid-catalyzed ethanol dehydration on zeolite is shown to proceed via a covalent ethoxy group (C2H5O) as a stable intermediate, which was directly observed by IR spectroscopy.