Abstract The XIAM code is one of the most frequently used programs to treat the microwave spectra of molecules with up to three methyl internal rotors. XIAM is user-friendly and fast, but often shows difficulties in dealing with low torsional barriers. An example is the case of m-methylanisole where the methyl group attached at the meta-position of the ring undergoes internal rotation with a barrier height of about 56 cm−1 for the cis conformer and 37 cm−1 for the trans conformer. The standard deviation obtained with XIAM is much larger than the measurement accuracy for both conformers. Recently, the code has been modified, and three higher order effective parameters connected to the potential term cos(3α) were implemented, which reduced the standard deviations of the fits to almost measurement accuracy.

中文翻译：

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XIAM 代码在模拟间甲基苯甲醚微波光谱方面的新水平成就

摘要 XIAM 代码是最常用的程序之一，用于处理具有多达三个甲基内转子的分子的微波光谱。XIAM 用户友好且速度快，但在处理低扭转障碍时经常表现出困难。一个例子是间甲基苯甲醚的情况，其中连接在环间位的甲基经历内旋，顺式构象异构体的势垒高度约为 56 cm-1，反式构象异构体的势垒高度约为 37 cm-1。使用 XIAM 获得的标准偏差远大于两种构象器的测量精度。最近对代码进行了修改，实现了与势项 cos(3α) 相关的三个高阶有效参数，这将拟合的标准偏差降低到几乎测量精度。