Department of Chemistry and Biochemistry, Queens College of the City University of New York, 65-30 Kissena Blvd., Queens, New York 11367, USA.
PhD Program in Chemistry, the Graduate Center of the City University of New York, 365 5th Ave., New York, New York 10016, USA.
Phys Chem Chem Phys. 2023 Jul 5;25(26):17370-17384. doi: 10.1039/d3cp02610h.
The 2-hydroxyethylhydrazinium nitrate ([HOCHCHNHNH]NO, HEHN) ionic liquid has the potential to power both electric and chemical thrusters and provide a wider range of specific impulse needs. To characterize its capabilities as an electrospray propellant, we report the formation of HEHN cluster ions in positive electrospray ionization (ESI) and their collision-induced dissociation. The experiment was carried out using ESI guided-ion beam mass spectrometry which mimics an electrospray thruster in terms of ion emission, injection into a vacuum and fragmentation in space. Measurements include compositions of primary ions in the electrospray plume and their individual dissociation product ion cross sections and threshold energies. The results were interpreted in light of theoretical modeling. To determine cluster structures that are comprised of [HE + H] and NO constituents, classical mechanics simulations were used to create initial guesses; and for clusters that are formed by reactions between ionic constituents, quasi-classical direct dynamics trajectory simulations were used to mimic covalent bond formation and structures. All candidate structures were subject to density functional theory optimization, from which global minimum structures were identified and used for construction of reaction potential energy surface. The comparison between experimental values and calculated dissociation thermodynamics was used to verify the structures for the emitted species [(HEHN)HE + H], [(HEHN)(HE) + H], [(HE) + H] and [(HE)CHOH] ( = 0-2), of which [(HE) + H] dominates. Due to the protic nature of HEHN, cluster fragmentation can be rationalized by proton transfer-mediated elimination of HNO, HE and HE·HNO, and the latter two become dominant in larger clusters. [(HE) + H] and [(HE)CHOH] contain H-bonded water and consequently are featured by water elimination in fragmentation. These findings help to evaluate ion formation and fragmentation efficiencies and their impacts on electrospray propulsion.
硝酸 2-羟乙基肼 ([HOCHCHNHNH]NO，HEHN) 离子液体有望为电动和化学推进器提供动力，并提供更广泛的比冲需求。为了表征其作为电喷雾推进剂的能力，我们报告了在正电喷雾电离 (ESI) 中形成 HEHN 团簇离子及其碰撞诱导解离。该实验是使用 ESI 引导离子束质谱法进行的，该方法在离子发射、注入真空和空间碎裂方面模拟了电喷雾推进器。测量包括电喷雾羽流中初级离子的组成及其各个解离产物离子的截面和阈值能量。结果根据理论模型进行了解释。为了确定由 [HE + H] 和 NO 组成的团簇结构，使用经典力学模拟创建初始猜测；对于由离子成分之间的反应形成的团簇，使用准经典直接动力学轨迹模拟来模拟共价键形成和结构。所有候选结构都经过密度泛函理论优化，从优化结果中确定了全局最小结构，并用于构建反应势能面。通过实验值与计算解离热力学的比较，验证了发射物种 [(HEHN)HE + H]、[(HEHN)(HE) + H]、[(HE) + H] 和 [(HE)CHOH]（=0-2）的结构，其中 [(HE) + H] 占主导地位。由于 HEHN 的质子性质，团簇碎裂可以通过质子转移介导的 HNO、HE 和 HE·HNO 的消除来合理化，在后两种情况下，在较大的团簇中占主导地位。[(HE) + H] 和 [(HE)CHOH] 含有氢键合水，因此在碎裂过程中以水消除为特征。这些发现有助于评估离子形成和碎裂效率及其对电喷雾推进的影响。
