We present measurements and calculations of the trap loss rate for laser cooled Rb atoms confined in either a magneto-optic or a magnetic quadrupole trap when exposed to a room temperature background gas of Ar. We study the loss rate as a function of trap depth and find that copious glancing elastic collisions, which occur in the so-called quantum-diffractive regime and impart very little energy to the trapped atoms, result in significant differences in the loss rate for the MOT compared to a pure magnetic trap due solely to the difference in potential depth. This finding highlights the importance of knowing the trap depth when attempting to infer the total collision cross section from measurements of trap loss rates. Moreover, this variation of trap loss rate with trap depth can be used to extract information about the differential cross section.Comment: 9 pages, 9 figure

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Control of the translational motion of methyl radicals is demonstrated by using pulsed magnetic fields created by a series of solenoid coils. By synchronously switching the magnetic fields corresponding to the motion of the radicals, we have observed the deceleration and focusing of a supersonic radical beam. The present result shows that Zeeman deceleration of polyatomic free radicals in the doublet state can be realized. This opens possibilities for trapping cold polyatomic free radicals in a spatially confined area leading to further studies of cold collisions and reactions.

Matrix-isolation spectroscopy in solid parahydrogen is a powerful technique for the study of photochemical reactions in detail. It is especially suited for the detection of chemical intermediates and unstable molecular products of photochemical reactions that are otherwise difficult to observe using other conventional spectroscopic techniques. Here, we have revisited UV photochemistry of benzene induced by 193 and 253.7 nm excitations by matrix-isolation infrared spectroscopy using solid parahydrogen as a host matrix. In addition to the formation of benzvalene, fulvene, and Dewar benzene as photoproducts of the UV photolysis of benzene, we have confirmed the production of cyclohexadienyl radical in solid parahydrogen as an intermediate species for a ring-opening reaction to 1,3,5-hexatriene. Moreover, we have identified 1,3-hexadien-5-yne and o-benzyne as minor products of the photochemical reaction. The reaction mechanisms of these species based on the analysis of FTIR spectra and quantum chemical calculations are discussed.

UV photodissociation of α-alanine was studied by parahydrogen matrix isolation infrared spectroscopy. The temporal behavior of Fourier transform infrared spectra revealed that UV irradiation at 213 nm yielded the HOCO radical as a direct photoproduct from the S 2 excited state. The concentration of HOCO quickly approached a steady state due to secondary photodissociation of HOCO to produce CO 2 + H or CO + OH. On the other hand, no photoproducts were detected by S 1 excitation at 266 nm. Irradiation of fully deuterated α-alanine at 213 nm yielded ∼2 times more cis-DOCO radicals than the lower energy isomer trans-DOCO, indicating that the conformation of the hydroxyl group is fairly well-preserved upon photodissociation of α-alanine. The present study suggests that HOCO may be a good tracer species in the search for amino acids in interstellar space.