Enhancement of spectroscopic instrumentation for investigation of molecular cluster dynamics

Enhancement of two spectroscopic instruments has been made for the purpose of increasing the sensitivity for detection and characterization of dimer and trimer clusters. The first instrument is a tunable infrared diode laser supersonic jet spectrometer involving high frequency modulation (HFWMS). Specifically, a second derivative technique is used via superposition of a modulation signal upon the ramp current. With the elimination of instrumental bandwidth limitations, the fundamental modulation frequency was increased by a factor of ten, resulting in a tenfold increase in signal-to-noise ratio. Further improvements were also made through an upgrade of the data acquisition system. The second instrument is a Bomem DA8 high resolution spectrophotometer applied to static gas phase and supersonic jet studies. In this case application of a high temperature argon arc source permitted the sensitivity of the instrument to be increased over that of a globar especially in the detector noise limited regime of an MCT detector compared to the source noise limited regime of an InSb.; Supersonic jet investigations of HBr dimer were made for the first time using the upgraded tunable diode laser spectrometer to illustrate its improved performance. The {dollar}nusb1sp{lcub}pm{rcub}{dollar} and {dollar}nusb2sp{lcub}pm{rcub}{dollar} tunneling bands of (H{dollar}sp{lcub}79{rcub}{dollar}Br){dollar}sb2{dollar}, (H{dollar}sp{lcub}79{rcub}{dollar}Br-H{dollar}sp{lcub}81{rcub}{dollar}Br), and (H{dollar}sp{lcub}81{rcub}{dollar}Br){dollar}sb2{dollar} were observed in the region 2500-2600 cm{dollar}sp{lcub}-1{rcub}.{dollar} The {dollar}nusb1sp{lcub}pm{rcub}{dollar} bands involved perpendicular transitions ({dollar}Delta{dollar}K{dollar}sb{lcub}rm a{rcub}{dollar} = {dollar}pm{dollar}1) while the {dollar}nusb2sp{lcub}pm{rcub}{dollar} bands are parallel type transitions ({dollar}Delta{dollar}K{dollar}sb{lcub}rm a{rcub}{dollar} = 0). The {dollar}nusb2sp+{dollar} broken symmetry band was also observed for the mixed dimer, giving an experimental value of 15.18(1) cm{dollar}sp{lcub}-1{rcub}{dollar} for the tunneling frequency of the ground state splitting as a result of the interconversion barrier.; Gas phase spectra of N{dollar}sb2{dollar}O and supersonic jet spectra of OC-HCl were recorded using high resolution (0.004 cm{dollar}sp{lcub}-1{rcub}{dollar}) FTIR spectroscopy with the argon arc source and the results were compared with those from a conventional 1535(20) K globar source. The performance of the argon arc source was also compared with results using the synchrotron source Max 1 at Lund, Sweden.