title: Simultaneous 13C/12C and (18)O/(16)O isotope ratio measurements on CO2 based on off-axis integrated cavity output spectroscopy.
abstract: A prototype off-axis integrated cavity output spectrometer (OA-ICOS) utilizing two identical cavities together with a near-infrared (1.63 microm) external cavity tunable diode laser is described. The two-cavity design-one for a reference gas and one for a sample gas-takes advantage of classical double-beam infrared spectrometer characteristics in reducing uncertainties due to laser scan or power instabilities and major temperature variations by a factor of three or better compared with a single-cavity scheme. This is the first OA-ICOS instrument designed to determine 13C/12C and (18)O/(16)O ratios from CO2 rotation/vibration fine structure in three different combination bands. Preliminary results indicate that at 0.8 Hz a precision of 3.3 and 2.8 per thousand is obtained for delta13C and delta(18)O, respectively, over a period of 10 h and a pure CO2 gas sample at 26 hPa. By averaging 100 spectra over a subset of the data, we achieved a precision of 1.6 and 0.8 \permil\ for delta13C and delta(18)O, respectively.
authors.affiliation: Bay Area Environmental Research Institute, Sonoma, CA 95476, USA. jost@baeri.org
authors.forename: Hans-Jürg
authors.initials: HJ
authors.lastname: Jost
authors.forename: Antonio
authors.initials: A
authors.lastname: Castrillo
authors.forename: H William
authors.initials: HW
authors.lastname: Wilson
mesh_terms: D002245:Carbon Dioxide / Q000737:chemistry*; D002247:Carbon Isotopes / Q000737:chemistry*; D006801:Humans; D010103:Oxygen Isotopes / Q000737:chemistry*; D015203:Reproducibility of Results; D017550:Spectroscopy, Fourier Transform Infrared / Q000295:instrumentation / Q000379:methods
chemical_list: D002247:Carbon Isotopes; D010103:Oxygen Isotopes; D002245:Carbon Dioxide