No abstract

This paper considers population transfer between eigenstates of a finite quantum ladder controlled by a classical electric field. Using an appropriate change of variables, we show that this setting can be set in the framework of adiabatic passage, which is known to facilitate ensemble control of quantum systems. Building on this insight, we present a mathematical proof of robustness for a control protocol-chirped pulse-practised by experimentalists to drive an ensemble of quantum systems from the ground state to the most excited state. We then propose new adiabatic control protocols using a single chirped and amplitude-shaped pulse, to robustly perform any permutation of eigenstate populations, on an ensemble of systems with unknown coupling strengths. These adiabatic control protocols are illustrated by simulations on a four-level ladder.

N 2 O removal was investigated in N 2 or air using 172 nm Xe 2 excimer lamps (50 or 300 mW/cm 2 ) without using any expensive catalysts. The residual amount of N 2 O and the formation ratios of products were measured as functions of photoirradiation time, N 2 O concentration, and O 2 concentration. N 2 O (100 ppm) was completely converted to N 2 and O 2 without NO x emission in N 2 at atmospheric pressure after 30 min photoirradiation using a high-power Xe 2 excimer lamp (300 mW/cm 2 ). 76% of N 2 O (100 ppm) was also converted to N 2 , O 2 , and HNO 3 in air (20% O 2 ) after 30 min photoirradiation using the high-power lamp. We concluded that N 2 O is dominantly decomposed by 172 nm photolysis in N 2 and by the O( 1 D) þ N 2 O reaction in air, where O( 1 D) atoms dominantly arise from the 172 nm photolysis of O 2 . The conversion of N 2 O in air increased more than twofold by decreasing the total pressure from atmospheric pressure to 20 kPa by suppressing the collisional quenching of O( 1 D) by N 2 and O 2 buffer gases. In a flow experiment, the conversion of N 2 O in N 2 was only 6 -18% in the total flow rate range of 0.1-1 L/min owing to the short residence time of N 2 O in the photolysis chamber.

The photochemical removal of NO, NO2, and N2O was investigated in N2 using a 146 nm Kr2 (25 mW cm−2) excimer lamp. The results obtained were compared with those obtained using 172 nm Xe2 (50 or 300 mW cm−2) excimer lamps. The removal rates of NO and NO2 at 146 nm were 11 and 36% slower than those at 172 nm, respectively. On the other hand, the removal rate of N2O at 146 nm was 21 times faster than that at 172 nm. The differences in the removal rates are discussed in terms of the absorption coefficient at each wavelength and effects of photoabsorption by N2 at 146 nm. By the addition of a small amount of O2 into an N2O/N2 mixture, the removal rate of N2O at 146 nm decreased greatly. On the basis of these facts, it was concluded that the 146 nm excimer lamp is especially useful for the N2O removal in N2 at atmospheric pressure.

Decomposition of NO2 (200 ppm) in N2 or air by 172-nm Xe2 excimer lamp was studied at 1 atm. The NO2 conversion in N2 was 99%, and the formation ratios of N2, O2, NO, and N2O were 47, 98, 0, and 2%, respectively, after 30 min irradiation. The NO2 in air (5–20% O2) could be completely converted to N2O5 and HNO3 due to reactions by O3 and H2O after only 1.0–1.5 min irradiation. The present results give a new simple photochemical aftertreatment technique of NO2 in air without using any catalysts.