title: A quantum cascade laser cw cavity ringdown spectrometer coupled to a supersonic expansion source.
abstract: A new instrument has been constructed that couples a supersonic expansion source to a continuous wave cavity ringdown spectrometer using a Fabry-Perot quantum cascade laser (QCL). The purpose of the instrument is to enable the acquisition of a cold, rotationally resolved gas phase spectrum of buckminsterfullerene (C(60)). As a first test of the system, high resolution spectra of the nu(8) vibrational band of CH(2)Br(2) have been acquired at approximately 1197 cm(-1). To our knowledge, this is the first time that a vibrational band not previously recorded with rotational resolution has been acquired with a QCL-based ringdown spectrometer. 62 transitions of the three isotopologues of CH(2)Br(2) were assigned and fit to effective Hamiltonians with a standard deviation of 14 MHz, which is smaller than the laser frequency step size. The spectra have a noise equivalent absorption coefficient of 1.4 x 10(-8) cm(-1). Spectral simulations of the band indicate that the supersonic source produces rotationally cold (approximately 7 K) molecules.
authors.affiliation: Department of Chemistry, University of Illinois, Urbana, Illinois 61801, USA.
authors.forename: Brian E
authors.initials: BE
authors.lastname: Brumfield
authors.forename: Jacob T
authors.initials: JT
authors.lastname: Stewart
authors.forename: Susanna L
authors.initials: SL
authors.lastname: Widicus Weaver
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Escarra
authors.forename: Scott S
authors.initials: SS
authors.lastname: Howard
authors.forename: Claire F
authors.initials: CF
authors.lastname: Gmachl
authors.forename: Benjamin J
authors.initials: BJ
authors.lastname: McCall