A single ro-vibrational line (P(1)) of HCN was measured at 6516.65402 cm -1 and its peak area was obtained relative to that of a single HC 3 N ro-vibrational line (R(5), centered at 6554.075 cm -1 ). Figure shows these two peaks, along with the Gaussian fits used to obtain the peak areas. where S ij (HCN) is the line intensity of the P(1) transition of HCN obtained at 20 K from HITRAN (1.6 × 10 -20 cm -1 /( molecule • cm -2 )), P is the partial pressure of each gas as prepared in the stock cylinder, and "area" is the area of the experimentally measured rovibrational peak for each molecule obtained by fitting the peak with a Gaussian function. The integrated area for the P(1) peak of HCN was 3.1 × 10 -9 cm -2 and the integrated area for the R(5) peak of HC 3 N was 2.6 × 10 -9 cm -2 , yielding a final line intensity of S ij (HC 3 N) = 1.2 × 10 -20 cm -1 /( molecule • cm -2 ) for this ro-vibrational transition at 20 K.