Objection 1. It would seem that not even a solemn vow dissolves a marriage already contracted. For according to a Decretal (cap. Rursus, De his qui cler. vel vovent.) "in God's sight a simple vow is no less binding than a solemn one." Now marriage stands or falls by virtue of the Divine acceptance. Therefore since a simple vow does not dissolve marriage, neither will a solemn vow dissolve it.
Objection 2. Further, a solemn vow does not add the same force to a simple vow as an oath does. Now a simple vow, even though an oath be added thereto, does not dissolve a marriage already contracted. Neither therefore does a solemn vow.
Objection 3. Further, a solemn vow has nothing that a simple vow cannot have. For a simple vow may give rise to scandal since it may be public, even as a solemn vow. Again the Church could and should ordain that a simple vow dissolves a marriage already contracted, so that many sins may be avoided. Therefore for the same reason that a simple vow does not dissolve a marriage already contracted, neither should a solemn vow dissolve it.
On the contrary, He who takes a solemn vow contracts a spiritual marriage with God, which is much more excellent than a material marriage. Now a material marriage already contracted annuls a marriage contracted afterwards. Therefore a solemn vow does also.
Further, the same conclusion may be proved by many authorities quoted in the text (Sent. iv, D, 28).
I answer that, All agree that as a solemn vow is an impediment to the contracting of marriage, so it invalidates the contract. Some assign scandal as the reason. But this is futile, because even a simple vow sometimes leads to scandal since it is at times somewhat public. Moreover the indissolubility of marriage belongs to the truth of life [Cf. I, 16, 4, ad 3; I, 21, 2, ad 2; II-II, 109, 3, ad 3], which truth is not to be set aside on account of scandal. Wherefore others say that it is on account of the ordinance of the Church. But this again is insufficient, since in that case the Church might decide the contrary, which is seemingly untrue. Wherefore we must say with others that a solemn vow of its very nature dissolves the marriage contract, inasmuch namely as thereby a man has lost the power over his own body, through surrendering it to God for the purpose of perpetual continence. Wherefore he is unable to surrender it to the power of a wife by contracting marriage. And since the marriage that follows such a vow is void, a vow of this kind is said to annul the marriage contracted.
Reply to Objection 1. A simple vow is said to be no less binding in God's sight than a solemn vow, in matters pertaining to God, for instance the separation from God by mortal sin, because he who breaks a simple vow commits a mortal sin just as one who breaks a solemn vow, although it is more grievous to break a solemn vow, so that the comparison be understood as to the genus and not as to the definite degree of guilt. But as regards marriage, whereby one man is under an obligation to another, there is no need for it to be of equal obligation even in general, since a solemn vow binds to certain things to which a simple vow does not bind.
Reply to Objection 2. An oath is more binding than a vow on the part of the cause of the obligation: but a solemn vow is more binding as to the manner in which it binds, in so far as it is an actual surrender of that which is promised; while an oath does not do this actually. Hence the conclusion does not follow.
Reply to Objection 3. A solemn vow implies the actual surrender of one's body, whereas a simple vow does not, as stated above (Article 1). Hence the argument does not suffice to prove the conclusion.
Source: Summa Theologica (New Advent)