[A primary study of 8-14 microm band emittance].

According to the previous experimental results, the band emittance of two materials were computed for 8-14 mm bandwidth in infrared measuring. The band emittance of several materials was surveyed by a simple experiment. The experiment and reckoning show that there is some kind of functional relation between band emittance and temperature. If the object measured is non-gray, and emissivity is regarded as a constant, acute measurement error will be generated for band pass radiation thermometer and thermal imaging system. The band emittance is nearly linear with the temperature for nonmetal and metal in vacuum by primary analysis. The fitted function equation can be used as the modification of band pass radiation thermometer and thermal imaging system, and the band emittance not only simplifies the calculation, but also improves the accuracy of measurement.

A TD-DFT study on the hydrogen bonding of three esculetin complexes in electronically excited states: strengthening and weakening.

Time-dependent density functional theory (TD-DFT) method was used to study the excited-state hydrogen bonding of three esculetin complexes formed with aprotic solvents. The geometric structures, molecular orbitals (MOs), electronic spectra and the infrared (IR) spectra of the three doubly hydrogen-bonded complexes formed by esculetin and aprotic solvents dimethylsulfoxide (DMSO), tetrahyrofuran (THF) and acetonitrile (ACN) in both ground state S(0) and the first singlet excited state S(1) were calculated by the combined DFT and TD-DFT methods with the COSMO solvation model. Two intermolecular hydrogen bonds can be formed between esculetin and the aprotic solvent in each hydrogen-bonded complex. Based on the calculated bond lengths of the hydrogen bonds and the groups involved in the formation of the intermolecular hydrogen bonds in different electronic states, it is demonstrated that one of the two hydrogen bonds formed in each hydrogen-bonded complex is strengthened while the other one is weakened upon photoexcitation. Furthermore, it is found that the strength of the intermolecular hydrogen bonds formed in the three complexes becomes weaker as the solvents change from DMSO, via THF, to ACN, which is suggested to be due to the decrease of the hydrogen bond accepting (HBA) ability of the solvents. The spectral shifts of the calculated IR spectra further confirm the strengthening and weakening of the intermolecular hydrogen bonds upon the electronic excitation. The variations of the intermolecular hydrogen bond strengths in both S(0) and S(1) states are proposed to be the main reasons for the gradual spectral shifts in the absorption and fluorescence spectra both theoretically and experimentally.

Rotational model for nematic phase stability of fluorinated phenylbicyclohexane liquid crystals.

A mechanical molecular rotation model for liquid crystal (LC) systems is employed to evaluate phase transition temperature of fluorinated phenylbicyclohexane isomeric LC compounds. Results show that when a fluorine atom is substituted along the molecular long axis, an LC molecule acquires high rotational speed and its rotation becomes stable, thereby resulting in a better thermal stability of the nematic phase. A novel explanation is proposed for the behavior of the nematic-isotropic phase of the LC system when a heavy atom is substituted along the molecular long axis.