Rotational spectra of vibrationally excited CCH and CCD.
The millimeter-wave rotational spectra of the lowest bending and stretching vibrational levels of CCH and CCD were observed in a low pressure discharge through acetylene and helium. The rotational, centrifugal distortion, and fine structure constants were determined for the (02(0)0) and (02(2)0) bending states, the (100) and (001) stretching levels, and the (011) combination level of CCH. The same pure bending and stretching levels, and the (110) combination level were observed in CCD. Apparent anomalies in the spectroscopic constants in the bending states were shown to be due to l-type resonances. Hyperfine constants, which in CCH are sensitive to the degree of admixture of the A 2Pi excited electronic state, were determined in the excited vibrational levels of both isotopic species. Theoretical Fermi contact and dipole-dipole hyperfine constants calculated by Peric et al. [J. Mol. Spectrosc. 150, 70 (1991)] were found to be in excellent agreement with the measured constants. In CCD, new rotational lines tentatively assigned to the (100) level largely on the basis of the observed hyperfine structure support the assignment of the C-H stretching fundamental (nu1) by Stephens et al. [J. Mol. Struct. 190, 41 (1988)]. Rotational lines in the excited vibrational levels of CCH are fairly intense in our discharge source because the vibrational excitation temperatures of the bending vibrational levels and the (110) and (011) combination levels are only about 100 K higher than the gas kinetic temperature, unlike the higher frequency stretching vibrations, where the excitation temperatures are five to ten times higher.
Infrared diode laser kinetic spectroscopy of the CCH radical ν3 band
Infrared diode laser kinetic spectroscopy was applied to the photodecomposition of acetylene at 193 nm to observe the ν3 (C–C stretching) band of the CCH radical. More than one hundred absorption lines were observed between 1750 and 1900 cm−1, but none of them could have been assigned to the ν3 band. This is probably due to CCH molecules being excited to high‐lying vibrational states by the excess energy of the photolysis. In fact, when either hydrogen or deuterium was added to acetylene as a buffer gas, new absorption lines appeared and were assigned to the ν3 fundamental band. The band origin which was derived from the observed spectrum is 1840.5711(4) cm−1, in agreement with the result of a previous matrix study. The spin–rotation interaction constant was found to decrease by as much as 30% upon ν3 excitation, presumably because of mixing with the lowest excited electronic state.
Engineering bio-inks for 3D bioprinting cell mechanical microenvironment
Three-dimensional (3D) bioprinting has become a promising approach to construct­ing functional biomimetic tissues for tissue engineering and regenerative medicine. In 3D bioprinting, bio-inks are essential for the construction of cell microenviron­ment, thus affecting the biomimetic design and regenerative efficiency. Mechanical properties are one of the essential aspects of microenvironment, which can be char­acterized by matrix stiffness, viscoelasticity, topography, and dynamic mechanical stimulation. With the recent advances in functional biomaterials, various engineered bio-inks have realized the possibility of engineering cell mechanical microenviron­ment in vivo. In this review, we summarize the critical mechanical cues of cell micro­environments, review the engineered bio-inks while focusing on the selection princi­ples for constructing cell mechanical microenvironments, and discuss the challenges facing this field and the possible solutions for them.