High-Sensitivity Raman Spectrometer To Study Pristine and Irradiated Interstellar Ice Analogs

Abstract

We discuss the novel design of a sensitive, normal-Raman spectrometer interfaced to an ultra-high vacuum chamber (5 × 10(-11) Torr) utilized to investigate the interaction of ionizing radiation with low temperature ices relevant to the solar system and interstellar medium. The design is based on a pulsed Nd:YAG laser which takes advantage of gating techniques to isolate the scattered Raman signal from the competing fluorescence signal. The setup incorporates innovations to achieve maximum sensitivity without detectable heating of the sample. Thin films of carbon dioxide (CO2) ices of 10 to 396 nm thickness were prepared and characterized using both Fourier transform infrared (FT-IR) spectroscopy and HeNe interference techniques. The ν+ and ν- Fermi resonance bands of CO2 ices were observed by Raman spectroscopy at 1385 and 1278 cm(-1), respectively, and the band areas showed a linear dependence on ice thickness. Preliminary irradiation experiments are conducted on a 450 nm thick sample of CO2 ice using energetic electrons. Both carbon monoxide (CO) and the infrared inactive molecular oxygen (O2) products are readily detected from their characteristic Raman bands at 2145 and 1545 cm(-1), respectively. Detection limits of 4 ± 3 and 6 ± 4 monolayers of CO and O2 were derived, demonstrating the unique power to detect newly formed molecules in irradiated ices in situ. The setup is universally applicable to the detection of low-abundance species, since no Raman signal enhancement is required, demonstrating Raman spectroscopy as a reliable alternative, or complement, to FT-IR spectroscopy in space science applications.

A photoionization mass spectroscopic study on the formation of phosphanes in low temperature phosphine ices

“…[15][16][17][18][19][20][21][22][23][24] Briefly, a silver mirror substrate is mounted onto a rotatable cold finger made of oxygen-free high-conductivity copper (OFHC) cooled to 5.5 K AE 0.1 by a closed-cycle helium refrigerator (Sumitomo Heavy Industries, RDK-415E). [15][16][17][18][19][20][21][22][23][24] Briefly, a silver mirror substrate is mounted onto a rotatable cold finger made of oxygen-free high-conductivity copper (OFHC) cooled to 5.5 K AE 0.1 by a closed-cycle helium refrigerator (Sumitomo Heavy Industries, RDK-415E).…”

FORMATION OF KETENE (H2CCO) IN INTERSTELLAR ANALOGOUS METHANE (CH4)-CARBON MONOXIDE (CO) ICES: A COMBINED FTIR AND REFLECTRON TIME-OF-FLIGHT MASS SPECTROSCOPIC STUDY

“…The experiments were carried out in a contamination-free ultrahigh vacuum (UHV) chamber ( Figure 1) evacuated to a base pressure of typically 2 × 10 −11 Torr using magnetically suspended turbo molecular pumps backed by an oil free scroll pump (Bennett et al 2013;Jones & Kaiser 2013;Kaiser et al 2014). A polished silver mirror is then mounted to the cold finger and interfaced with indium foil to ensure thermal conductivity and subsequently cooling to a final temperature of 5.5 ± 0.1 K; the entire ensemble is freely rotatable within the horizontal center plane and translatable in the vertical axis via an UHV compatible bellow (McAllister,BLT106) and differential pumped rotational feed through (Thermoionics Vacuum Products, RNN-600/FA/MCO).…”

Uv-Vis, Infrared, and Mass Spectroscopy of Electron Irradiated Frozen Oxygen and Carbon Dioxide Mixtures With Water

“…The experiments were carried out in a novel contaminationfree ultra-high vacuum experimental setup at the newly established W. M. Keck Research Laboratory in Astrochemistry (Bennett et al 2013;Jones & Kaiser 2013). The main chamber of the instrument is typically evacuated down to a base pressure of 5 × 10 −11 torr using oil-free magnetically suspended turbomolecular pumps and dry scroll backing pumps.…”