The Spectroscopy of Hydrogen Nitrogen Oxygen, Methane and Isotopically Substituted Methanes in the Near Infrared

In this work we investigate the near infrared spectra of several small polyatomic molecules. The first was observed in the 12987-13513 cm^{ -1} range while recording the Delta v = 4 H_2O_2 overtone band. Comparison of high resolution scans and asymmetric top computer simulations determined the existence of the HNO free radical within the photoacoustic apparatus. The second molecule is methane (^{12}CH_4) whose 3 nu_1 + nu_3 vibrational overtone spectrum was recorded at room temperature, 100 K and approximately 15 K using laser intracavity photoacoustic and molecular beam techniques. Although rotational congestion renders the room temperature spectrum undecipherable, the 100 K data suggest possible ro-vibrational assignments confirmed in the molecular beam spectrum by their temperature dependences. Molecular beam Stark spectroscopy is used to unambiguously identify the E symmetry components of the R(2), P(2) and Q(2) transitions. These results suggest the presence of other bands whose intensities are derived through interactions with the 3nu_1 + nu_3 transition. Quantitative analysis of these interactions suggests a bright state origin of 11277.0 cm^{-1}. Lastly, the room temperature and 100 K Deltav = 4 overtone bands of the isotopically substituted methanes, ^{13}CH_4 , ^{12}CH _3D, ^{12}CH _2D_2, ^{12}CHD_3 and ^{13}CHD_3 are recorded and compared to the ^ {12}CH_4 results. Analysis of the ^{13}CH _4 3nu_1 + nu_3 spectrum suggests that it too consists of several bands that derive their intensity from a single bright state. The deuterated methane overtone bands become more rotationally and vibrationally complex as the number of C-H oscillators is increased.