Abstract
We measured Raman spectra of N(2) fluids obtained at 0.1-25 MPa at room temperature. The (14)N(15)N peak in the Raman spectrum of a low-pressure N(2) fluid is difficult to detect because of the prevalence of a group of peaks attributed to rotational vibration of (14)N(2). The Raman peaks of (14)N(15)N and (14)N(2) of N(2) fluid at 25 MPa were acquired at various exposure times. The mean values and standard deviations of the peak height ratios and peak area ones of (14)N(15)N and (14)N(2) were examined for each time. The standard deviations of the peak height ratios and peak area ones were 2.2% and 1.9%, respectively, for 20 spectra acquired with peak height of 1 million counts of (14)N(2). The uncertainties are about two times higher than those predicted from the noise of a CCD. Improvement of the pixel resolution can enhance the precision of the nitrogen isotope ratios by Raman spectroscopy.