Electronic-vibrational dynamics and coherence in x-ray transient absorption of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mi mathvariant="normal">N</mml:mi><mml:mn>2</mml:mn><mml:mo>+</mml:mo></mml:msubsup></mml:math>

Attosecond transient absorption spectroscopy (ATAS) is becoming an indispensable and powerful tool in the emerging field of attochemistry, while the interpretation of measurements often requires full considerations of the coupling among various freedoms of motion. Here we develop the ionization-coupling model to incorporate the transient absorption and explore the coupled electronic-vibrational dynamics of nitrogen ions induced by strong-field ionization. It is found the coherent vibrational wave packet on the involved electronic state is created with a broad distribution of vibrational levels, which leads to the spectral overlap on the <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mi>K</a:mi></a:math>-edge absorption. By identifying the contributions of each electronic state, the study reveals the significant role of the excited state <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"><b:mrow><b:msup><b:mi>A</b:mi><b:mn>2</b:mn></b:msup><b:msub><b:mi mathvariant="normal">Π</b:mi><b:mi>u</b:mi></b:msub></b:mrow></b:math>, differing from previous work by <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"><d:mi>K</d:mi></d:math>-edge absorption measurements []. We uncover features of absorption from forbidden transitions within the laser pulse duration and confirm the vibronic coherence-induced quantum beating of absorption. A scheme is proposed to avoid the spectral overlap and determine the population distribution among the states, which is crucial to resolve the debate on nitrogen air lasing. This work lays down the framework to research the ionic coherence in ATAS and offers valuable insights into the intricate interplay between electronic and vibrational dynamics.