The reaction mechanism of Br2 ＋ I2 = 2IBr was investigated at the （U）MP2/3-21G^＊ level, and one four-centred transition state as well as two three-atom molecules （IBr2,I2Br） were thus obtained. The same result w...The reaction mechanism of Br2 ＋ I2 = 2IBr was investigated at the （U）MP2/3-21G^＊ level, and one four-centred transition state as well as two three-atom molecules （IBr2,I2Br） were thus obtained. The same result was achieved by comparing the activation energy of three reaction paths, i.e., the minimum activation energy of the bimolecular elementary reaction Br2 ＋ I2 = 2IBr is less than the dissociation energy of Br2 or I2. It is thus theoretically proved that the title reaction occurs more easily in the bimolecular form without light initiation. However, once the reaction system was initiated by light through the reaction path of Br atom reacting with I2 or I atom reacting with Br2, the title reaction was completed quickly, which was verified with absorbance measurement at 516 nm in the present study.展开更多
Traditional studies on potential yield mainly referred to attainable yield： the maximum yield which could be reached by a crop in a given environment. The new concept of crop yield under average climate conditions wa...Traditional studies on potential yield mainly referred to attainable yield： the maximum yield which could be reached by a crop in a given environment. The new concept of crop yield under average climate conditions was defined in this paper, which was affected by advancement of science and technology. Based on the new concept of crop yield, the time series techniques relying on past yield data was employed to set up a forecasting model. The model was tested by using average grain yields of Liaoning Province in China from 1949 to 2005. The testing combined dynamic n-choosing and micro tendency rectification, and an average forecasting error was 1.24%. In the trend line of yield change, and then a yield turning point might occur, in which case the inflexion model was used to solve the problem of yield turn point.展开更多
基金Project supported by the Chinese Post Doctoral Research Fund (No. 2003033486)
文摘The reaction mechanism of Br2 ＋ I2 = 2IBr was investigated at the （U）MP2/3-21G^＊ level, and one four-centred transition state as well as two three-atom molecules （IBr2,I2Br） were thus obtained. The same result was achieved by comparing the activation energy of three reaction paths, i.e., the minimum activation energy of the bimolecular elementary reaction Br2 ＋ I2 = 2IBr is less than the dissociation energy of Br2 or I2. It is thus theoretically proved that the title reaction occurs more easily in the bimolecular form without light initiation. However, once the reaction system was initiated by light through the reaction path of Br atom reacting with I2 or I atom reacting with Br2, the title reaction was completed quickly, which was verified with absorbance measurement at 516 nm in the present study.
基金Supported by Agricultural Poor-helping Monopoly of Graduate University of Chinese Academy of Science (40641002)
文摘Traditional studies on potential yield mainly referred to attainable yield： the maximum yield which could be reached by a crop in a given environment. The new concept of crop yield under average climate conditions was defined in this paper, which was affected by advancement of science and technology. Based on the new concept of crop yield, the time series techniques relying on past yield data was employed to set up a forecasting model. The model was tested by using average grain yields of Liaoning Province in China from 1949 to 2005. The testing combined dynamic n-choosing and micro tendency rectification, and an average forecasting error was 1.24%. In the trend line of yield change, and then a yield turning point might occur, in which case the inflexion model was used to solve the problem of yield turn point.
