Investigation of the heterogeneous reactivity of HCl, HBr, and HI on ice surfaces

Journal Article · Thu Dec 02 04:00:00 EST 1999 · Journal of Physical Chemistry A: Molecules, Spectroscopy, Kinetics, Environment, amp General Theory

DOI:https://doi.org/10.1021/jp990400c· OSTI ID:20013057

Barone, S B; Zondlo, M A; Tolbert, M A

The interactions of hydrogen halide gases (HX = HCl, HBr, and HI) with thin ice films representative of atmospheric aerosols have been studied using a Knudsen cell reactor coupled to a Fourier transform infrared-reflection absorption (FTIR-RAS) spectroscopic probe. The gas-phase uptake and reaction products resulting from the exposure of hydrogen halides to ice surfaces over a wide range of temperatures (110--210 K), hydrogen halide partial pressures (5--1,000 x 10{sup {minus}7} Torr), and ice film thicknesses (10--100 nm) are reported. Studies of HCl and HBr showed efficient reactions on crystalline and amorphous microporous ice films at 110 K to form H{sub 3}O{sup +} until reaching coverages ranging from (5--20) x 10{sup 15} molecules cm{sup {minus}2}, after which the rate of reaction dramatically decreased. The uptake of HCl on hexagonal crystalline ice at temperatures representative of the lower stratosphere and upper troposphere (180--210 K) was found to depend strongly on HCl partial pressure. Over the temperature range studied, exposure of ice to HCl partial pressures below the HCl equilibrium partial pressure at the liquid/ice coexistence point resulted in uptake limited to (3.5 {+-} 1.6) x 10{sup 15} molecules cm{sup {minus}2}. In contrast, exposure to HCl pressures larger than the HCl equilibrium partial pressure resulted in unlimited uptake. HBr and HI were efficiently and continuously taken up by ice surfaces ({gamma} {ge} 0.02) over a range of atmospherically relevant temperatures (180--210) K. Although crystalline hydrates of HX:H{sub 2}O are stable over the temperature range examined, the incorporation of hydrogen halides into ice always resulted in the formation of amorphous HX:H{sub 2}O product layers with the exception of HBr uptake at high flow rates (flow rate {ge}3.1 x 10{sup 15} molecules s{sup {minus}1}) which resulted in the formation of a mixture of crystalline hydrates.

• Research Organization: George Washington Univ., DC (US)
• OSTI ID: 20013057
• Journal Information: Journal of Physical Chemistry A: Molecules, Spectroscopy, Kinetics, Environment, amp General Theory, Journal Name: Journal of Physical Chemistry A: Molecules, Spectroscopy, Kinetics, Environment, amp General Theory Journal Issue: 48 Vol. 103; ISSN 1089-5639; ISSN JPCAFH
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
AMORPHOUS STATE
CRYSTALS
FILMS
HYDRIODIC ACID
HYDROBROMIC ACID
HYDROCHLORIC ACID
ICE
STRATOSPHERE
SURFACES