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外文期刊>The Astrophysical journal
>A Theory Attributing Optical Diffuse Interstellar Absorption Bands, “Unidentified Infrared” Emission Bands, and Cloud Reddening to H2 Nonlinear Absorption
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A Theory Attributing Optical Diffuse Interstellar Absorption Bands, “Unidentified Infrared” Emission Bands, and Cloud Reddening to H2 Nonlinear Absorption
A theory is described that attributes the diffuse interstellar absorption bands (DIBs) to coherently driven two-photon absorption by H2 molecules present in sheetlike clouds located near hot stars. Results from three-level nonlinear spectroscopy are used to argue that vacuum ultraviolet (VUV) photons from the star impinging on the H2-containing cloud will be primarily absorbed in simultaneous two-photon (Raman-type) transitions, resulting in the build-up of coherent VUV Stokes-wave radiation in the "plane" of the H2-containing cloud on the transitions [Cn X0; P(2) and P(3) ; n = 0–5] and on some of the transitions [Bn X0 , P(2) and P(3)]. Via this in-plane VUV Stokes-wave radiation, para-hydrogen molecules in the (X0, J'' = 2) level and ortho-hydrogen molecules in the (X0, J'' = 3) level are coherently excited to levels [Cn(Πu+); J' = 1 and 2 ; n = 0–5] and [Bn, J' = 1 and 2], which thus serve as the intermediate states in resonantly enhanced, coherently driven, two-photon absorption. The DIBs result from visible light from the star being simultaneously absorbed in "second step" transitions from the coherently excited (C, B)-state levels to various singlet gerade state levels.In-plane coherent VUV Stokes-wave radiation at [Cn X0; P(2) and P(3); n = 1 ? 5] can also act to produce in-plane coherent IR radiation via stimulated Raman scattering processes terminating on various EF singlet gerade levels. Striking coincidences are shown to exist between frequencies of IR Stokes-wave transitions expected to be strong and those of the so-called unidentified infrared emission bands (UIBs). Assuming a common identity, assignments are offered for most of the known UIBs.More than 70 sharp DIBs are assigned to transitions from B- and C-state levels to levels of singlet gerade states. On the basis of in-plane four-wave mixing of VUV and IR-Stokes-waves radiation (i.e., four-wave parametric generation), the most prominent features seen in the emission spectrum of the Red Rectangle are also explained. It is furthermore indicated that cloud reddening should be an additional manifestation of the presence of intense, in-plane, VUV Stokes-wave radiation.
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机译：描述了一种理论，该理论将星际弥散吸收带（DIB）归因于位于热恒星附近的片状云中存在的H2分子相干驱动的双光子吸收。三级非线性光谱的结果被用于论证，来自恒星撞击在含H2的云上的真空紫外线（VUV）光子将主要在同时发生的两个光子（拉曼型）跃迁中被吸收。相干的VUV斯托克斯波辐射在跃迁[Cn X0; P（2）和P（3）; n = 0-5]，并且在某些过渡上[Bn X0，P（2）和P（3）]。通过该平面VUV斯托克斯波辐射，（X0，J''= 2）能级的对氢分子和（X0，J''= 3）能级的原氢分子被相干激发到[ Cn（Πu+）; J'= 1和2; n = 0-5]和[Bn，J'= 1和2]，因此在共振增强，相干驱动的双光子吸收中充当中间状态。 DIB是由于来自恒星的可见光同时在“第二步”中吸收而从相干激发（C，B）态跃迁到各种单重态gerade态而产生的。[Cn X0 ; P（2）和P（3）; n = 1？ [5]还可以通过终止于各种EF单线态gerade水平的受激拉曼散射过程来产生面内相干IR辐射。事实表明，预期的IR斯托克斯波跃迁频率与所谓的未识别的红外发射带（UIB）的频率之间存在惊人的巧合。假设具有相同的身份，则会为大多数已知的UIB提供分配.70多个清晰的DIB被分配给从B状态和C状态级别到单重态Gerade状态级别的转换。基于VUV和IR-斯托克斯波辐射的面内四波混合（即四波参数生成），还解释了红色矩形发射光谱中最突出的特征。还表明，云变红应该是强烈的，平面内的VUV斯托克斯波辐射的存在的另一种表现。
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