Resonant infrared irradiation of CO and CH 3 OH interstellar ices
Resonant infrared irradiation of CO and CH 3 OH interstellar ices
复制标题
CO和CH 3 OH星际冰的共振红外辐射
DOI：
10.1051/0004-6361/202245704
复制
发表时间：
2023
影响因子：
6.5
通讯作者：
Santos J
中科院分区：
文献类型：
--
作者：
Santos J
上下文涉及冰尘埃颗粒的固相光过程通过导致复杂有机分子的形成和诱导光解吸作用极大地影响星际介质的化学演化。到目前为止，实验室研究的重点主要是高能紫外（UV）光子对冰的影响，但红外（IR）光子的直接振动激发预计也会影响星际冰的形态和含量。然而，人们对这种多余的振动能量耗散的机制以及它对结构和冰光化学的影响仍然知之甚少。在这项工作中，我们提出了一个系统的调查星际相关的CO和CH3OH冰类似物的振动模式的共振激发后，使用可调红外辐射的行为。我们试图量化的IR诱导的光解吸，并获得洞察振动能量耗散对冰形态的影响。我们利用了一个在低温下的真空装置来生长纯CO和CH3OH冰，以及两者的混合物。我们将冰暴露在强烈的，近单色的中红外（MIR）自由电子激光辐射中，使用FELIX自由电子激光设施的丽莎终端站选择性地激发物种。冰的变化是通过反射吸收红外光谱法结合四极质谱法监测的。这些方法也使我们能够表征光解吸效率。振动能量的耗散被观察到是高度依赖于激发模式和冰的化学环境。所有的无定形冰在共振辐射下都经历了某种程度的重组，形成了更有组织的结构。此外，在纯CO和CH3OH冰中都观察到了IR诱导的光脱附，星际光脱附效率约为10个分子cm−2s−1。该结果与UV诱导的对应物的结果相当或更高。还观察到在冰混合物中CH3OH的振动激发时CO的间接光解吸，特别是在富含甲醇的环境中。在这里，我们讨论了这些IR诱导的现象的天体化学影响。
Context. Solid-phase photo-processes involving icy dust grains greatly affect the chemical evolution of the interstellar medium by leading to the formation of complex organic molecules and by inducing photodesorption. So far, the focus of laboratory studies has mainly been on the impact of energetic ultraviolet (UV) photons on ices, but direct vibrational excitation by infrared (IR) photons is expected to influence the morphology and content of interstellar ices as well. However, little is still known about the mechanisms through which this excess vibrational energy is dissipated, as well as its implications for the structure and ice photochemistry.Aims. In this work, we present a systematic investigation of the behavior of interstellar relevant CO and CH3OH ice analogs following the resonant excitation of vibrational modes using tunable IR radiation. We seek to quantify the IR-induced photodesorption and gain insights into the impact of vibrational energy dissipation on ice morphology.Methods. We utilized an ultrahigh vacuum setup at cryogenic temperatures to grow pure CO and CH3OH ices, as well as mixtures of the two. We exposed the ices to intense, near-monochromatic mid-IR (MIR) free-electron-laser radiation using the LISA end-station at the FELIX free electron laser facility to selectively excite the species. Changes to the ice are monitored by means of reflection-absorption IR spectroscopy combined with quadrupole mass-spectrometry. These methods also allowed us to characterize the photodesorption efficiency.Results. The dissipation of vibrational energy is observed to be highly dependent on the excited mode and the chemical environment of the ice. All amorphous ices undergo some degree of restructuring towards a more organized configuration upon on-resonance irradiation. Moreover, IR-induced photodesorption is observed to occur for both pure CO and CH3OH ices, with interstellar photodesorption efficiencies on the order of 10 molecules cm−2s−1. This result is comparable to or higher than what is found for UV-induced counterparts. An indirect photodesorption of CO upon vibrational excitation of CH3OH in ice mixtures is also observed to occur, particularly in environments that are rich in methanol. Here, we discuss the astrochemical implications of these IR-induced phenomena.