Relaxation Of Collision Between Highly Excited HBr(DBr) Molecules And Gas Molecules

In the process of relaxation of the excited state molecules,laser-induced chemical reaction and combustion,the collision energy transfer of the molecular vibrational excited state plays an important role.The energy transfer rate coefficient between states and states can be used to predict heat transfer and thermalization rates.Studies of hydrogen halides and rare gas atoms can provide valuable benchmark data.The analysis of the operation of the HBr optical pump laser under non-equilibrium conditions and the practical application of the HBr high power laser require in-depth experimental and theoretical research on the collision energy transfer process between the HBr molecular vibration states.In addition,hydrogen halide is a marker for volcanic eruptions and earthquake events.Studies of hydrogen halides and rare gas atoms are very important for the prediction of these natural phenomena.There are many researches on oxygen and alkali metal hydrides at home and abroad,and there are few studies on the collision between hydrogen halide molecules and gases.The research on HBr molecules is mostly focused on the energy transfer of low vibration states.There was no relevant research report on the collision transfer between DBr molecules and other gas molecules.Therefore,we conducted further experimental studies on the vibrational relaxation of HBr?DBr?molecules.In this paper,degenerated depolarized super Raman pump is used to stimulate the high vibrational state of the DBr molecule to the ground electronic state v??=8,and it relaxes with other collision gases?Ar,D₂?.For DBr?v??=8?and Ar mixed systems,the evolution of time-resolved populations of vibrational state v??=8 of DBr molecules after collisional relaxation is detected by high-resolution instantaneous laser-induced fluorescence and the total pressure remains unchanged.By changing the molar ratio of collision gas,the coefficient of relaxation rate of DBr?v??=8?and inert gas Ar was found to be k₈?Ar?=?0.51±0.1?×10^-1212 cm³molecule^-1s^-1.For DBr?v??=8?and D₂ mixed systems,the collisional relaxation rate of DBr?v??=8?molecules with D₂ was obtained using a method similar to the above DBr?v??=8?and Ar collisional relaxation.The coefficient is k₈?D₂?=?3.50±0.8?×10^-12cm³molecule^-1s^-1.For DBr and D₂ mixed systems with a molar ratio of 0.5,The OPO laser pumped YAG laser excites DBr molecules to X¹?⁺v??=8 vibrational state,then the time evolution of LIF intensity of DBr v??=8,7,and 6 vibration states are measured.The rate of DBr vibrational state v??=8 relaxing to the v??=6 is faster than that of DBr vibrational state v??=8 relaxing to the v??=7.The time evolution curve of LIF intensity of DBr vibrational state v??=6shows a clear bimodal structure.The measurement results show that the double quantum relaxation occurs in the collisional relaxation of DBr?v??=8?and D₂.The pump light excites the DBr molecules to X¹?⁺v??=7 vibrational state,and the temporal dynamics of the LIF intensity of the three vibrational states of DBr v??=7,6,and 5 are measured.The results are similar to the DBr?v??=8?,and a double quantum relaxation also occurs in the collisional relaxation of DBr?v??=7?and D₂.The laser excites the HBr molecule to the vibrational state v??=5 of the ground electronic state.We studied the collisional relaxation process of HBr?v??=5?and HBr,CO₂,H₂.In a pure HBr system,the relaxation rate of HBr?v??=5?at different pressures was measured,and the coefficient of self-relaxation rate k_v??=5 of the HBr molecular vibrational state v??=5 was obtained as?2.10±0.6?×10^-12cm³molecule^-1s^-1.When the sample pool temperature is 295K and the pressure is 200Pa,the time evolution curves of fluorescence intensity induced by HBr vibrational state v??=5,4 and 3 are measured.Based on the rate equation,the collisional transfer rate coefficients of HBr molecules are obtained which are k_5,3=?5.20±0.9?×10^-13cm³molecule^-1s^-1 vibrational state v??=5?v??=3 and k_4,3=?1.10±0.3?×10^-12cm³molecule^-1s^-1 for vibrational state v??=4?v??=3 respectively.From the measurement results,we can get that the sum of k_5,4 and k_5,3 accounts for 95%of k₅,so the probability of multiple quantum relaxation in HBr self relaxation is very small.The temperature of the sample cell was changed and the self-relaxation rate coefficients of HBr?v??=5?were measured.The results showed that the self-relaxation rate coefficient increases with increasing temperature.In the mixed gas of HBr molecules and CO₂ molecules,the molar ratio of carbon dioxide is changed,and the time evolution of the population of HBr vibrational state v??=5 is measured.The relaxation rate coefficient of HBr?v??=5?with CO₂ molecules is obtained to be k₅?CO₂?=?5.34±0.9?×10^-12cm³molecule^-1s^-1.k_5,4?CO₂?can be obtained by the rate equation,it is?5.10±0.9?×10^-12cm³molecule^-11 s^-1.Its value is very close to k₅?CO₂?,there is basically only single quantum relaxation.At different cell temperatures,the collisional relaxation rate coefficient of HBr?v??=5?and CO₂ was measured and it was found that the relaxation rate coefficient decreases slightly with increasing temperature.For the HBr?v??=5?and H₂ mixed system,the relaxation rate coefficient k₅?H₂?of HBr?v??=5?can be obtained by the method similar to the above HBr?v??=5?and CO₂ collisional relaxation.k₅?H₂?is?4.00±0.8?×10^-13cm³molecule^-1s^-1,and the rate coefficient k_5,3?H₂?of HBr molecular vibrational state v??=5 relaxation to vibrational dynamic v??=3 is?3.70±0.8?×10^-13cm³molecule^-1s^-1,k_5,3?H₂?and HBr?v??=5?is very close,basically only two quantum relaxation of?v=2 occurs in the collision of HBr?v??=5?with H₂.This experimental results can not be well explained by SSH theory.The coefficient of collisional relaxation rate of HBr?v??=5?and H₂ increases rapidly with increasing temperature.