Spectrochimica Acta Part A 80 (2011) 75–81 Contents lists available at ScienceDirect Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy j ourna l ho me page: www.elsevier.com/locate/saa Remote-Raman spectroscopic study of minerals under supercritical CO 2 relevant to Venus exploration Shiv K. Sharma a,∗ , Anupam K. Misra a , Samuel M. Clegg b , James E. Barefield b , Roger C. Wiens b , Tayro E. Acosta a , David E. Bates a a Hawaii Institute of Geophysics and Planetology, SOEST, University of Hawaii, Honolulu, HI 96822, USA b Los Alamos National Laboratory, P.O. Box 1663, MS J565, Los Alamos, NM 87545, USA a r t i c l e i n f o Article history: Received 12 August 2010 Received in revised form 17 January 2011 Accepted 23 January 2011 Keywords: Remote Raman spectroscopy Minerals Supercritical carbon dioxide Venus mineralogy a b s t r a c t The authors have utilized a recently developed compact Raman spectrometer equipped with an 85 mm focal length (f/1.8) Nikon camera lens and a custom mini-ICCD detector at the University of Hawaii for measuring remote Raman spectra of minerals under supercritical CO 2 (Venus chamber, ∼102 atm pres- sure and 423 K) excited with a pulsed 532 nm laser beam of 6 mJ/pulse and 10 Hz. These experiments demonstrate that by focusing a frequency-doubled 532 nm Nd:YAG pulsed laser beam with a 10× beam expander to a 1 mm spot on minerals located at 2 m inside a Venus chamber, it is possible to measure the remote Raman spectra of anhydrous sulfates, carbonates, and silicate minerals relevant to Venus explo- ration during daytime or nighttime with 10 s integration time. The remote Raman spectra of gypsum, anhydrite, barite, dolomite and siderite contain fingerprint Raman lines along with the Fermi resonance doublet of CO 2 . Raman spectra of gypsum revealed dehydration of the mineral with time under super- critical CO 2 at 423 K. Fingerprint Raman lines of olivine, diopside, wollastonite and -quartz can easily be identified in the spectra of these respective minerals under supercritical CO 2 . The results of the present study show that time-resolved remote Raman spectroscopy with a compact Raman spectrometer of moderate resolution equipped with a gated intensified CCD detector and low power laser source could be a potential tool for exploring Venus surface mineralogy both during daytime and nighttime from a lander. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Remote Raman spectroscopy (RS) has been proposed as a poten- tial mineralogical analysis system to explore Venus [1,2]. This technique has several distinct advantages over other spectroscopic techniques, which have been used on past missions. For planetary applications, the sharpness of Raman spectral features of minerals allows for much less ambiguous detection, especially in the pres- ence of mixtures. Visible, near-infrared, thermal, and reflectance and emission spectroscopy of minerals and compounds all suf- fer from broad overlapping spectral features [3], which complicate interpretation of their spectra from which more than one miner- alogical solution can be typically derived. Small portable remote Raman systems, which are suitable for planetary rovers and lan- ders, have been shown to be effective in identifying hydrous and anhydrous minerals, glasses of mineral composition, and ices. Most of the remote Raman systems have been tested to a distance of 120 m [4–7]. Two of the most important advantages of remote ∗ Corresponding author. Tel.: +1 808 956 8476; fax: +1 808 956 3188. E-mail address: sksharma@soest.hawaii.edu (S.K. Sharma). Raman spectroscopy over other techniques for a mission to Venus are rapid mineralogical analysis of both hydrous and anhydrous minerals and stand-off analysis at distances up to many meters [8]. Rapid mineralogical analysis and stand-off analysis are important to missions to Venus due to the harsh environment on the planet surface (pressure ∼9.1 MPa (90 atm) and temperature ∼735 K) [9]. The major gas in the Venus atmosphere is CO 2 , and under Venus atmospheric conditions CO 2 exists in the supercritical phase near the surface. Remote Raman measurements conducted at the Uni- versity of Hawaii on minerals under high temperatures up to 1003 K at 9 m, and under supercritical CO 2 (∼95 atm and 423 K) at 1.5 m have successfully demonstrated the potential of the tech- nique for Venus exploration. Previous high-temperature Raman spectroscopy work on minerals has shown that high tempera- tures can have a strong effect on the Raman spectra of minerals [2,10,11]. These temperature effects include broadening of Raman lines, decrease in intensity of Stokes–Raman lines, phase transitions in minerals, and the dehydration and decarbonation of minerals. At high temperatures the broadening of the Raman lines is caused by an increase in the degree of anharmonicity of vibrational modes. The observed negative shifts in the position of Raman lines of silicate minerals with temperature are caused by an increase in 1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2011.01.033