China
Africa
Explore chapters and articles related to this topic
Elementary Processes of Excited Molecules and Atoms in Plasma
Published in Alexander Fridman, Lawrence A. Kennedy, Plasma Physics and Engineering, 2021
Alexander Fridman, Lawrence A. Kennedy
The typical value of a rotational constant is 10−3–10−4 eV, which means, that at room temperatures, the quantum number J is about 10. As a result, in this case, even the largest rotational quantum is relatively small, about 5*10−3 eV. In contrast to the vibrational quantum, the rotational one corresponds to low values of the Massey parameter Eq. (2.37) PMa = ΔE/ħαv = ω/αv even at low gas temperatures. This means, that the energy exchange between rotational and translational degrees of freedom is a fast non-adiabatic process (see Section 2.2.7). As a result, the rotational temperature of molecular gas in plasma is usually very close to the translational temperature even in non-equilibrium discharges, while vibrational temperatures can be significantly higher.
Section 5: Flow Modeling for a Plasma Assisted Diamond Deposition Reactor
Published in Mark A. Prelas, Galina Popovici, Louis K. Bigelow, Handbook of Industrial Diamonds and Diamond Films, 2018
K. Hassouni, C. D. Scott, S. Farhat
Energy transfer between the translational and rotational modes of the heavy particles is very fast and leads to, in moderate pressure plasmas, an equilibrium between these modes [Bird, 1976] and [Brun, 1986]. As a consequence, the rotational distribution functions of all the molecular species are Boltzmann distributions with a rotational temperature equal to the translational temperature. The equilibrium between the translational and rotational modes of the heavy particles leads to a description of these modes in terms of one temperature which is usually called the gas temperature Tg.
Unexpected coexistence of radiation and absorption in rotationally excited nitrogen molecular ions
Published in Journal of Modern Optics, 2021
Rongbo Su, Fujun Wang, Guiping Dan, Wu Kang, Zhaoyi Tan, Jingjie Ding
Further, we try to understand the fact that the appearance of the absorption is about 250 fs later than the radiation as marked by the Δt in Figure 1(a). When the rotational temperature is 300 K, absorption dominates the region from 391.15 nm to 391.3 nm. However, the rotational temperature is rather higher than the room temperature at the initial time of the plasma generation [32–34], leading to the molecular nitrogen ions populating in higher rotational quantum states. Population inversion in the rotational states with quantum numbers from 19 to 23 is achieved, which recompenses the absorption resulted from the rotational transitions from these states with the rotational quantum numbers from 1 to 5. Hence, only radiation was observed during the initial 250 fs after the generation of plasma. To gain further insight into the underlying mechanism of the experimental observations,the time evolution of the rotational temperature needs to be understood over several picoseconds. Rotational temperature is often aimed to approach the translational temperature of the gas species in the discharge experiments [35,36]. In these studies, the rotational temperature was extracted from high-resolution rotational spectra of the first negative system of by fitting the spectral intensity of both P and R branch emission. However, the rotational temperature is discussed in the dense plasma at a typical time scale of nanosecond [37], and the result in the underdense plasma induced by femtosecond laser pulse has not been reported yet. Recently, Yao et al. found that the equilibrium temperature is 300 K in the resonant Raman amplification experiment [20]. In this paper, we consider that the rotational temperature T decays to 300 K with a initial in a picosecond. As is well known, and are generated by tunnel ionization of the outermost and inner-valence electrons of the nitrogen molecules, respectively [19]. The rotational distribution of states and mainly inherit the rotational distribution of nitrogen molecules. The pump laser can raise the rotational temperature of several hundred K by a non-resonant Raman process [32]. Thus, the initial rotational temperature is set to be 1100 K in this simulation, and it decreases to the room temperature 300 K rapidly in 1 ps, as shown in Figure 3(a).