The formation of N2O nanoparticles in a collisional cooling cell between 4 and 110 K

Abstract

published as an Advance Article on the web 3rd August 2001 particles covering a vast size range from some nanometres up to some hundred nanometres were N 2 O (CO 2 ) formed by injecting gaseous into a collisional cooling cell at temperatures between 4 and 110 K. N 2 O (CO 2) FTIR spectroscopy was used to study the vibrational dynamics of the nanoparticles between about 600 and 4000 cm~1. For the spectra of the bigger particles formed at temperatures around 78 K, we have studied the inÑuence of the experimental conditions on the Ðne structure of the strong absorption bands and its temporal behavior. From an estimate of the particle sizes, we conclude that the observed changes in the Ðne structure are not simple size e †ects ; they are likely to be due to a change in the particle shape or in the molecular order. From a comparison with infrared spectra of clusters generated in a supersonic jet expansion, we estimate the size of the particles produced at temperatures below 10 K to lie around one nanometre.

Infrared spectroscopy of (CO2)N nanoparticles (30<N<14500) flowing in a uniform supersonic expansion

“…For comparison, the ratio concerning the very large clusters (Nϳ10 11 ) observed at 90 K in Ref. 10 reaches 1:0.3 while the value of 1:0.8 is reported for CO 2 solid films at 77 K. 39,40 Again, the relatively high amplitude associated with the peak around 655 cm Ϫ1 ͑peak 1͒ in the work by Kunzmann et al 12 is linked to large (CO 2 ) N particle radii estimated to lie below 100 nm.…”

“…7,10,12 These techniques lead to rates of cooling, nucleation, and growth different from those associated with supersonic expansions, affecting the degree of crystallinity, size, and morphology of the particles formed. These, in turn, may affect the widths of absorptions, the appearance of extra structures in the spectra, and the relative intensities of these features.…”

“…Aerosols are formed by collisional cooling in cryogenic cells maintained either at liquid-nitrogen [6][7][8][9][10][11] or even at liquid-helium temperatures. 1,12 The intermediate cluster size range (10 4 ϽNϽ10 9 ) has received less attention since it requires either much higher stagnation pressures 13 or a very dilute quantity of CO 2 sample in the cooled buffer gas of a cryogenic cell, thus requiring the use of multireflection optical devices to lengthen the absorption path. 1,14,15 This work deals with nanometric clusters much smaller than the wavelength of the infrared light used to probe them so that the extra structures observed by Gough et al [8][9][10][11] in the case of aerosols and interpreted by them on the basis of the Mie model 16 are not visible in our spectra.…”

Self-Diffusion in Core-Shell CompositeCO212/CO2<

“…To investigate processes of small molecular particles in the time scale of seconds to hours [2,3] collisional cooling techniques in combination with Fouriertransform infrared (FTIR) spectroscopy have become effective methods [4 -9]. These processes comprise shape evolution, phase transitions, binary diffusion, and chemical and physical reactions of the particles.…”

Infrared spectroscopy of solid mixed ammonia–water and acetylene–water aerosol particles

“…temperature and pressure of the bath gas in the cell and the concentration of sample gases injected into the cell) [34,40,42,43,50]. The size of aerosol particles can be estimated from their IR spectra and a detailed summary of the effects of particle size on IR spectra can be found in the paper by Sigurbjörnsson et al [1].…”